I am releasing the first version of linux device driver for xbox 360 audio. you can get source from here: http://www.megaupload.com/?d=SVAUYFBL. The device driver is alsa compitable, so basically you can compile mplayer and then it should play various music formats for you easily. It supports both analog stereo and digital spdif (only dobly digital by now). Thanks for tmbinc for his finding on 360 audio hardware details and his help on debuging the code. The license for the code is GPL.