:masturboy:
There really is no such thing. Sans gutting cats, 99.9999% of dealers could care less about exhaust. MAG does quite a few exhaust installs on any given month, and are pretty mod friendly in my experience. There really is no grounds to void your power train warranty for a simple catback. Intakes tend to raise red flags, but they are worthless on just about any Audi.
Get Awe Touring, sit back and listen to that sweeeeeet music.