After working at a local Audi dealer in the service dept I saw several A4 1.8t's come in with after-market exhaust systems.  There are several that don't fit well at all, are too loud and weigh too much.  After much review of what's out there I bought the complete system from Techtonics Tuning.  I am very impressed!  It's fits well...no clearance problems at all.  The sound is just a bit louder than stock and no resonance. The ground clearance is the best.  The system weighs 30 lbs less than stock.  It works very well with my GIAC 1.0 bar chip.  As a very picky 43 yr old VW/Audi nut and the proud owner of several cherry VW's and a Audi.  "I'm very happy with the $600.00 I spent on the exhaust!" It offered me the best bang for the buck.