I can recommend Foobar, if it's possible to setup to automatically start streaming. It has a transparent-sounding audio path in it. You can use "sc" from the command line to make ~any program run as a service by the way. But for non-CLI software it might be a better idea to have the machine auto-login and have it somewhere that autoruns after login. Let me know if you try it as a service, if it works or not. (i don't know if it would show the GUI after logging in, if you run it at boot, before logging in) One benefit of a service running even after login is that it can restart itself if it crashes.
It's hard to believe that only the Exstreamer 1000 has a digital output on it.