Pro-Ject Audio Systems Stream Box S2 Ultra network bridge

I have reviewed several network-connected music servers in recent years, from Antipodes, Aurender, and NAD. All performed well but are relatively expensive, and their associated player apps didn’t equal Roon’s user friendliness in terms of interface, organization of the library, and inclusion and updating of metadata. So when Roon Labs introduced their own server, the Nucleus+, I first reviewed and then purchased it, along with a lifetime subscription to Roon. But at $2498 without an internal drive for storing music files, the Nucleus+ is still relatively expensive, and even Roon’s less-powerful Nucleus costs $1398. I was still on the lookout for a server that would be more accessible to our budget-minded readers.

Jim Austin and Jason Victor Serinus are using Roon with servers based on Intel’s low-cost NUC computer-on-a-board, and there are other suitable processors, such as the Raspberry Pi and the various Arduinos. But the last two are hardly fit’n’forget for the average audiophile—I was looking to review a lower-cost turnkey solution.

Then, when Pro-Ject’s US distributor, Sumiko Audio, sent us the Pre Box S2 Digital D/A headphone amplifier, which Ken Micallef reviewed in our April 2019 issue, they also sent a sample of the Austrian company’s Stream Box S2 Ultra, which costs $849.

Ah-ha—here was a product that appeared to offer what I was looking for in an affordable server and network bridge.

Into the Box
The Stream Box S2 Ultra is the same size as the tiny Pre Box S2 Digital: 4.1″ wide by 4.1″ deep by 1.4″ high. Unlike that D/A headphone amp, the Stream Box’s front panel has no display—just a USB Type A port, two buttons, and two LEDs. The rear panel is busier, with two more USB A ports, one marked DAC and optimized for audio signals, with a dedicated internal power supply and audiophile-grade components; Ethernet and HDMI ports; a jack for the external 18V DC power supply (supplied); and a jack for the wireless antenna. There’s also a recessed button marked Boot and a micro-USB port labeled Bypass. The front- and the other rear-panel Type A USB ports can be used to play files on external drives. When you press the front panel’s right-hand button, marked USB/PC, the rear-panel Bypass port “detoxes” that input—ie, it buffers and reclocks USB data when connected to a laptop or PC with the DAC port connected to a D/A processor (though the Stream Box can’t then be used as a network player).

Designed by John Westlake (footnote 1), whom I believe was also responsible for the Pre Box S2 Digital, the Stream Box S2 is based on the industrial Compute Module 3 version of the Raspberry Pi processor and runs a customized Volumio operating system. The operating system is installed on 12.79GB of onboard memory, which also can be used to store audio files. The file system supports PCM signals of resolutions up to 32-bit/352.8kHz, and DSD up to DSD256; all audio data are fed through to the USB-connected DAC.

The Stream Box S2 Ultra is controlled either by a Web browser or by a free iOS app, both of which support Tidal and Spotify streaming. The app’s home screen allows the Stream Box to access the user’s music library, whether it resides on the network, on USB sticks, or on the internal memory. The Stream Box incorporates Shairport, which allows you to stream audio from an iDevice, and is DLNA enabled and Roon Ready—ie, it can be used as a Roon endpoint. The HDMI port can used to connect a monitor that will echo the Web or iOS graphic user interface, which shows the album-cover art for the track playing.

The Stream Box S2 Ultra ran warm—after a few days of use, its top panel had stabilized at 99.5°F (37.5°C). So while its small size and lack of physical controls mean it can be tucked away in a closet, it will still need some ventilation.

After powering up the Stream Box S2 Ultra by plugging in the supply, then pressing the left-hand button and waiting for it to turn blue, I connected the Pro-Ject to my router. After a short while the Stream Box’s blue network LED lit up, and I connected its DAC USB output to our review sample of Pro-Ject’s Pre Box S2 Digital D/A processor. (Who thinks up these names?) Powering the Pre Box S2 Digital via the USB bus, Sumiko’s Buzz Goddard told me, “gives the benefit of two sets of power-filtration circuits, since the Stream Box has pretty tight filtering and regulation which the Pre Box then benefits from.” I then followed the instructions in the manual to find the Config Wizard on my iPad mini, which allowed me to choose the language, name the Stream Box, select a WiFi network, select the Pre Box S2 Digital as the audio output device, and enable it as a Roon endpoint.

As always with modern audio components, the first thing the Stream Box did after being turned on was to update its firmware and system software. I then launched the Pro-Ject Play iPad app, and selected a skin for the screen (the options feature Pro-Ject products). The Stream Box found the internal file storage on my Roon Nucleus+, and I was ready to play music.

Footnote 1: Scroll down the page here.