Just got my player 100% functional with a DAC that provides optical out to my receiver. My raspberry pi runs squeezelite, which streams FLAC from attached NAS and Logitech Media Server. I also installed shairport, which makes the pi an AirPlay receiver-now all iOS devices can stream music directly to it.
I wrote a few deamon scripts that startup squeezelite and shairport on startup, so the entire thing is headless and is controlled from the squeezeplayer iOS app.
I'm planning on putting it in a case with a switching power suppy to make it really pro-looking.
pi, DAC, squeezelite, and shairport