I've got the mixer working, Squeezeslave was trying to set the PCM volume instead of the master volume.

Playing a ~192kbit VBR MP3 consumes 20-40% of the CPU. I'm not sure if this is normal or not, but at least it seems like things are not on the verge of disaster. There is a stutter when changing tracks which I can get rid of with a bit of a delay; I'd like to come up with a better solution. I've tested Ogg Vorbis and FLAC and those are working too.

Now I'm working on the button input and I think I've got that figured out using /dev/ir. Also I need to get the player to shut down when the accessory power goes away, and /dev/empeg_power seems to be the trick to that one.