It also mentions API docs at their website for making your own UPnP apps. Under a section called 'Geeks read this' it mentions a Telnet command line interface on port 4444. It also has a built-in web controller for setup and playback. It is extremely tedious as you can imagine. You can use the included remote for setup and to browse the connected server library.

It has an LCD 'vacuum fluorescent' (?) display that shows the currently playing track, time, progress, and level meters. You could set up Internet Radio stations, too! Supported protocols/software are Windows Media Connect, iTunes, UPnP, Rhapsody (via UPnP), MusicMatch (UPnP), SlimServer. Supported bit depths are 8 and 16, mono or stereo. A note elsewhere says it supports 5.1 DTS and Dolby Digital via digital outputs. Supported audio formats are MP3, WMA, WMA lossless (converted to PCM), WAV, AIFF, LPCM, ALAC, FLAC, Ogg-Vorbis (via SqueezePlay). The manual says it has a 20 bit DAC (chip unknown), minimum line output of 2.83 volts, THD of -90db typical, and dynamic range of 90db typical, signal to noise ratio of 96db, frequency response of 20khz. It has coax/optical S/PDIF outs, and a 3.5 mm analog stereo out and included a RCA 'Y' adapter. It has ethernet (100BaseT) and wi-fi (802.1b) for connecting to your network. It cost about $200 at the time, and its feature set rivals many modern streamers. I still have the original packing stuff, and bonus, an actual printed User Guide with detailed instructions, diagrams, screen shots, and everything. It is long since abandoned, but I'm guessing if I hooked it up it would still work. I got it in 2005, so it's about 16 years old. This was Roku's first(?) product way back before there was any such thing as video streaming. I was rummaging around the other day and found my old streamer, a Roku SoundBridge M1000.

Roku upnp player