I just installed the Milltek A6 Avant Exhaust (purchased through Stratmosphere, Rush NY) onto my new 05 Allroad 4.2. Better gas mileage and more power were evident immediately and the sound levels (inside the car) differ only slightly from the original. The exhaust system replaced the original perfectly.

I spoke with Audi reps about chipping the engine and the effect that may have on the warrantee. I was told it would only effect the warrantee where the chip may cause an engine problem; that's pretty subjective and I'm holding off to see what options there are for further upgrades to help this engine flow more freely.