I have worked with DTM Autowerks on several occasions with our 03 A6 4.2 and they are everything you could want in Mechanic. They are knowledgeable, reasonably priced, and willing to work with you. They have saved me a ton of money over using a dealer or a mechanic who doesn't know Audi's. They are VW/Audi enthusiasts as well. Here's their website, it's not the best but all you really need is their #:

http://www.vwtuningnh.com/

I am in no way related to their business, I'm just a satisfied customer. They are in the middle of Milford NH...