I would like to replace my '96 A4 Bose head unit (AM/FM cassette) with a Bose CD head unit. Is this possible if I got one from an Audi dealer? Would it be a simple swap? I understand the new A4s have a Bose CD head unit as an option. I really didn't want to put a CD changer in the trunk. Any comments/help on this would be greatly appreciated.