the site http://www.cus.org.uk/~cleggy/ has A LOT of info on Unilink. THey have sorted the Computer used as a CD Changer with a headunit, and mapped out nearly all of the commands used on the bus. There is someone on the BBS that has done a computer controlling a changer, but the main emphasis of their project is a mp3 changer emulator.

I, like yourself, am interested in the empeg controlling a changer unit.