Stock radio questions

I now have a 2001 A4 1.8T Q Tiptronic with a symphony head unit. It didn't have the changer installed and I am trying to put in a Cd Changer that can play MP3's. Anyone out there done this yet? I have found adapter cables for the audi changer cable to certain manufacturer's changers, but none of them seem to match up. If any one can help me out here i'd be greatful, Thanks.