AudioQuest Dragonfly Cobalt

Stream Box S2 Ultra Review

The Universal Solution For Hi-Res Streaming In Your Home




  • Future-proof Your Favorite DAC
  • Raspberry Pi Inside & Roon Endpoint
  • USB Detox Device

Company & Product Overview

If you are reading this review, then you’re probably looking for a way to integrate your DAC into your network. You might already have a great DAC in your audio setup, and if you do, you're in luck. Any 2 channel music fan with a high-end DAC who doesn't want to waste money on a streamer with a DAC built-in will find the Stream Box worthy of considering.

But, trust us — you have never seen anything like the little Stream Box S2 Ultra. Pro-Ject’s Stream Box S2 Ultra, featured in today’s review, is an excellent example of the company’s unique ability to offer the most connectivity and performance compared to anything else on the market.

If you store a substantial library of hi-res music files on hard drives, USB sticks, or NAS storage devices, and you're looking for the best way to get these devices into your network with Roon compatibility and MQA, then Pro-Ject has something very interesting for you. For $849, it offers the most flexibility and the largest feature-set in a single device we have ever seen.

For anyone not familiar with the brand, Pro-Ject Audio is the world leader for high-performance turntables and cool micro-sized high-end components that are eye-catching and fun to listen to. At Audio Advice, we get excited about brands that create musically satisfying products without you having to spend a ton of money — with their unique manufacturing facilities based in the Czech Republic and Slovakia, Pro-Ject achieves the perfect balance.

Since 1990, the brand has brought astonishing products to the world of high-end audio at reasonable prices. Winning more than 100 awards from all over the world, including 10 ESIA awards, and the Red Dot Design Award, clearly, the brand knows what success is made of.

Stream Box S2 Ultra, itself, won the EISA’s 2018-2019 Best Product of the year. It's a very special “toolbox” for high-end audio that completely transforms any USB DAC into a wireless streamer. While it can fulfill a multitude of other functions, its main goal is to be the device that can get any USB DAC into the network.

But, before we get into this review, it’s important to note that the Stream Box S2 Ultra needs a DAC, a headphone amp, or a receiver with a USB input to operate.

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If you’re in the market for a proper DAC/headphone amp, Pro-Ject designed the Pre Box S2 Digital to complement your little streaming toolbox. Even though the goal of Stream Box S2 Ultra is to connect universally with any DAC, when you pair the streamer with its twin brother, you get a powerful DAC/headphone amp that greatly enhances the presentation of details hiding in the music for a great deal.

For $399, we think the Pro-Ject Pre Box S2 Digital is the perfect way to make headphones or powered speakers come alive with Pro-Ject’s little streamer — and for less than $1,300 for the bundle, they not only deliver great sound together and perfect connectivity; they’re aesthetically similar so they will look sharp sitting next to each other on your desk or a tabletop. Together, we think they become the most versatile and audiophile setup combo in this price class.

Of course, with the Stream Box S2 Ultra, you’re free to use any USB DAC that you’d like — but that’s only one of the cool things this little universal streamer can do!

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Design & Build Quality

Interestingly, Pro-Ject products have been used as props in countless TV shows and movies. When you look at their high-performance turntables, that comes as no surprise. Each product the company creates is made from scratch, by hand — down to the tiniest screw. Everything made in its European facilities is designed to be visually pleasing — and the little Stream Box S2 Ultra doesn’t disappoint.

Pro-Ject is not your typical manufacturer. The company is vertically integrated, so it can do all of its manufacturing in-house. We tip our hats to Heinz Lichtenegger, the company’s founder, for establishing the R&D headquarters outside Vienna, Austria where it neighbors two of its highly specialized manufacturing plants.

Pro-Ject has two divisions. One facility in the Czech Republic specializes in all things turntables. The other focuses on small home audio components that are known for over-delivering for their size. The Stream Box S2 Ultra is made in Slovakia in a highly specialized facility that’s dedicated to small home audio components.

As the universal toolbox for high-end audio, the Stream Box S2 Ultra packs a ton of cool ways for you or your guests to connect with the music you want to stream without overblowing it with unnecessary features. Pro-Ject achieves all of this connectivity in a small, simple, but beautiful little box that’s well crafted from the inside out.

The build quality feels solid, and yet it weighs less than a pound. The chassis is made from solid machined-aluminum and it comes in a black or silver finish. Every interaction with the product feels first-class. Even the button caps are made from machined-aluminum, which gives the unit a high-quality feel. It’s a little over 4-inches long, about 4-inches wide and almost 1.5-inches tall. The main body of the unit is square with sharp-looking geometry and streamlined edges that are simple and modern.

You’d be proud to display the unit on a desk or a tabletop right next to your DAC, computer, or any other piece of equipment in your audio setup. If you’re into gear with matching aesthetics, we think the little streamer looks slick next to its DAC twin brother, the Pre Box S2 Digital. Sleek, modern, and minimalistic.

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On the front panel, there’s a USB-A input for quick convenient connection with USB thumb drives or external hard drives. There are also two circular machined-aluminum push buttons — one larger push-button toggles the unit on and off, and a smaller push-button lets you toggle between two different modes. Also, from the front panel, three LED lights will illuminate blue or red showing you the status of the unit.

The back of the unit hosts the rest of the inputs and outputs for an assortment of uses. From left to right, they are — a dedicated USB-A output (marked “DAC”) that will let you connect any DAC into the network, another USB-A port for connecting USB storage drives, an Ethernet port that’s recommended for high-resolution playback, an HDMI video output to connect a monitor, a power adapter input which accepts 18 volts to provide power for the unit, and finally a special micro-USB input marked “Bypass” will accept a USB connection for pristine sounding playback with computers or laptops. The unit also comes with a dedicated internal power supply.

In the box, a detachable antenna is included, which screws onto the back of the unit to help your little streamer find and connect with your home’s wireless network. Essentially, once the unit connects to your WI FI at home, other smart devices can be connected on the network too — wirelessly! The sleek little box has the power to upgrade and future proof your favorite USB DAC with modern streaming capabilities. That alone is really cool. But, as you’ll see in the next section, there’s so much more going on inside.

AudioQuest Dragonfly Cobalt Computer

Features & Technology

With so many people embracing internet streaming services such as Tidal, Spotify, and Qobuz, many tech-savvy music lovers are getting interested in network-enabled audio products to help them integrate the playlists they created with other sources of music too. Most great sounding products in high-performance audio don’t offer network ability because they’re outdated or it wasn’t their main focus. The problem this creates is that we have to keep replacing our old outdated gear and keep buying new modern devices.

One solution has always been to simply do without and make compromises using our smartphone or tablet to stream poor quality audio over Bluetooth or connect the analog output to powered speakers or amps. There never really was a good solution for us — until now.

The Stream Box S2 Ultra has many uses for all things high-end audio. Inside, a collection of handy tools allow you to connect a wide range of network-enabled smart devices over WIFI, Bluetooth, Airplay, Ethernet, or USB with bit-perfect audio quality.

In terms of devices that can be networked to “play” wirelessly with Stream Box S2 Ultra, the list of playback options possible is endless… Connect any smartphone, tablet, computer, laptop, universal DLNA NAS drive, and any USB storage device. Just load up your library of hi-res music onto a USB stick, connect your favorite DAC, and start streaming! Plus, as a fully Roon Ready and certified device, Stream Box S2 Ultra can be used as a Roon endpoint too!

AudioQuest Dragonfly Cobalt Computer

In terms of playback, all signals are sent to the DAC via the USB audio output — letting Stream Box S2 Ultra play any audio file that your DAC can handle, including Tidal’s MQA. Stream Box S2 Ultra acts as a universal network bridge, bypassing the files directly to your digital-to-analog converter, so you won’t run into file-support issues. If your DAC can decode MQA, then Stream Box S2 Ultra will present whole MQA encoded music streaming with Tidal to your DAC. Essentially, if your external USB DAC can handle it, Stream Box S2 Ultra will unpack it.

The file system management software built inside of Stream Box S2 Ultra supports PCM files up to 32bit/352kHz and DSD256. The Stream Box S2 Ultra can also be used with all the popular streaming services, including Spotify, Tidal, Qobuz, and TuneIn internet radio with potential support for more being added all the time.

Sure, the Bluesound Node 2i can output digital audio at a lower price and it's also Roon Ready, but what sets the Stream Box apart is that the USB output allows for MQA and higher transfer rates. Most products have Toslink and Digital Coax outputs, but no streamers at this price-point have what the Stream Box has.

Inside the unit, a powerful Raspberry Pi computer no larger than a credit card will let you manage all these remote playback options. This is done using the Linux-based control software baked inside, which runs on top of a version of the Volumio operating system to give you command central-style oversight of your music for a variety of playback options.

AudioQuest Dragonfly Cobalt Computer

Control your playback from a web browser with any computer on your network, or download the new remote control app to remote control it from any iOS or Android mobile device. You can even use Roon!

Being Roon Ready and certified means Roon users can use the Stream Box as a Roon endpoint if you’d rather use Roon’s powerful software interface. As a Roon endpoint, Roon users can pick their Stream Box S2 Ultra within the Roon software and send high-resolution audio streams over the network with bit-perfect audio quality. For us, this is what living the dream sounds like!

With multi-room support for up to six devices, whether it’s with Roon, a DLNA compatible networked NAS that stores your entire music collection, a friend’s USB thumb drive plugged into the front panel, or your favorite streaming service, the little Stream Box S2 Ultra integrates all of it. The Volumio software can see Tidal, Qobuz, Spotify, or web radio playing directly from the Stream Box Ultra. So, when you select either Bluetooth or iOS input in the Stream Box Ultra’s software, you can Bluetooth directly to the unit from your Android phone or any Apple iOS device using Airplay.

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And if all this isn’t enough control over the music for you, Stream Box S2 Ultra can be used in standalone mode too. When you’re ready to interact with the unit like a computer or a tablet, the HDMI video output lets you connect an external monitor or touch screen to see your music library and manage playback of everything just like a computer.

AudioQuest Dragonfly Cobalt Computer

This scenario is particularly useful for those times you want more tactile control over your music library. It’s the perfect solution for anyone interested in a platform-agnostic interface. Just plug in a mouse and connect a keyboard to either of the two USB inputs and your little control hub is always ready — at your command. We think power users will have the most fun using the HDMI port with a touch screen instead for the best hands-on control experience.

There’s even a hard-wired “USB clarifier mode” that will clean the digital audio signal coming from your computer. When you station the unit in-between your computer and any USB DAC, it bypasses the noisy signal of your computer’s USB port and turns it into a USB “detox” device for ultra-clear sounding audio. This lets you “detoxify” the noise from the USB signal before it reaches the DAC for pristine sounding audio. We think this feature is so cool! It’s accessible right from the front panel with the dedicated push button marked “USB/PC.”

AudioQuest Dragonfly Cobalt Computer


Setting up our Stream Box S2 Ultra started fairly straightforward. In the beginning, there were a few speed bumps along the way getting it to connect with our wireless network, but in hindsight that was our user error. At Audio Advice, we explore the setup process to save you the headache. So, let us save you some time — for example, it helps if you enter the right password to the home network during the initial setup! Check out our Getting Started Guide for a quick rundown on how to get up and running, quickly.

To test the Stream Box S2 Ultra in a few different scenarios, we set it up with our wireless network first and then connected a Chord Mojo to the dedicated USB DAC port. Then we streamed hi-res music files stored on a USB thumb drive plugged directly into the front panel of the unit. We also used Qobuz to stream CD-quality music from a laptop to see how it performed with streaming services.

Mojo owners don’t need us to tell you how amazing it sounds, but for anyone else, check out our Mojo DAC Review for our impressions.

Next, we stationed the little Stream Box S2 Ultra between our laptop and our external USB DAC with a hard-wired USB connection to hear how the special micro-USB “detoxifier” feature sounds when the noise in our digital audio signal is purified with “Bypass” mode.

We used the Grado Labs RS2e Reference Series Over-Ear Headphones which is a great sounding headphone for listening to music at home. As an open-back headphone, it provides a wide-open soundstage with musical dynamics and ultra-smooth top-end.

We listened to a lot of styles of music without the special USB purifier mode activated to give us a good sense of how the music sounded just coming out of our DAC. Then, we tested the same music again with the USB purifier mode activated.

While everything sounded great no matter how we listened, one of the tracks that stood out the most improved was “Should I Stay or Should I Go,” released in 1982 by the new-wave punk outfit, The Clash. Immediately, we noticed significant improvements to the soundstage with crystal clear details. As a rock song recorded in the era of 80’s punk rock, this recording is characteristically “noisy” — probably by intention.

Recorded to analog tape, there’s a lot of inherent noise and other subtle nuances in the recording’s rhythm and pacing, overall — giving this track a great punk rock attitude. So, it surprised us when we heard how much clearer and detailed the overall presentation was when we listened to it with the USB purifier feature activated.

With the Stream Box S2 Ultra in bypass mode “cleansing” the USB signal coming out of our laptop, we were impressed by how much clearer the details were in the stereo image compared to a direct USB connection between the DAC and our laptop. The separation of details presented a little bit more depth and clarity to our stereo image too. To be completely upfront, we were skeptical at first. We truly didn’t expect this much improvement to the soundstage.

While the improvements were subtle, having access to the extra level of clarity and separation of details really drew us deeper into the music. The low-end rhythm and pacing and tuneful sense of timing were more musical. The separation of details were just a tad bit more spread apart, which let us hear the picking of guitar strings and other musical dynamics even clearer.

The vocal also stood out presently with more holographic realism. We enjoyed it so much, we made the USB “bypass” mode one of our go-to configurations for our listening session — we really couldn’t have it any other way!

AudioQuest Dragonfly Cobalt Computer

Overall Recommendation

All we can say is that adding the Stream Box S2 Ultra to your home audio setup will open up many possibilities for you to enjoy wireless freedom with your favorite DAC. If the Chord Poly extends the functionality and feature-set for the Chord Mojo, then you can think of the Stream Box S2 Ultra as Pro-Ject’s “universal Chord Poly.” The biggest difference being that Stream Box S2 Ultra isn’t limited to just one DAC — Stream Box S2 Ultra will extend the functionality and feature-set of any USB DAC. If you are a 2 channel music fan with a high-end DAC, and you don’t want to waste your money on a streamer with a built-in DAC, Stream Box is definitely for you.

If you’re looking to upgrade to a good DAC or a headphone amp, we think Pro-Ject Pre Box S2 Digital is the perfect DAC/headphone amp companion for the little Pro-Ject streamer. Go for the Pro-Ject bundle and snag this ultimate setup for a great price.

For the price, Pro-Ject Stream Box S2 Ultra offers the most flexibility and the largest feature-set in a single product we’ve ever seen. If you use hard drives, USB sticks, or a NAS to store a library of hi-res music, and looking for the best universal device that acts as a network to get all of it connected for an affordable price, we can’t imagine who wouldn’t choose this.

With Roon, DLNA from the NAS, WIFI, Ethernet, Bluetooth, AirPlay, HDMI, and two USB ports for storage devices, a keyboard or a mouse, there’s really no limit to what you can do with this magical little toolbox. We were blown away by how much value can be packed inside! With this, you are free to take control of your music in every square foot of your home.

It’s the ultimate toolbox for high-end audio — and for just $849, it’s a fantastic deal for a dedicated computer that gives you this much connectivity and control over your music.

  1. stream box s2 ultra front panel Pro-Ject Stream Box S2 Ultra Network Streamer

Sound Signature: From Musical to Analytical, the possibilities are limitless! It depends on your favorite DAC.

Who it’s for: Music Lovers.

What it’s for: Any Kind Of Music.

How to get peak performance: At Home.


AudioQuest Dragonfly Cobalt High Note 1

Future-proof Your Favorite DAC

Gives modern streaming capabilities to any USB DAC — a truly universal toolbox for high-end audio that will transform your favorite DAC into a streamer.

AudioQuest Dragonfly Cobalt Highnotes 2

Raspberry Pi Inside & Roon Endpoint

Tiny, but mighty. With the power of Raspberry Pi, you will never run out of ways to connect your devices and take control of your music. It might be small, but this toolbox has the largest feature-set we’ve seen at this price-point.

AudioQuest Dragonfly Cobalt Highnotes 3

USB Detox Device

“Cleansing” circuitry clarifies the noisy USB output from your computer or smart device, giving you a pristine home audio experience for you and your guests to enjoy.

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