The PES supercharger is done for my model, 02 a6 4.2 I've spoken with them I can definately purchase it.

 

VF Performance has superchargers for the S4/RS4 B6/B7 platforms. Might wanna check with them

 

I only see two listings for Audi on their site euro. Both are for the 2.0
You see something else?

 

Here are forums for supercharging an audi, direct questions could more easily be answered there: http://www.scaudi.com/sc/

 

I dont think its on their site but I know that there are S4's with them already on AZ. You can give them a call and ask about pricing, performance #'s and stuff. I know it runs up close to $10,000, and they offer financing. lol