Try to search for Sportec on the net: it's a Swiss tuner with some great offers for various Audis.. I love their alloy wheels!
Here is a small pic for a start:
http://www.audirs6.ch/tuning/bilder/...s6_avant_1.jpg
And the specs

550 hp and 635 Nm
Not cheap anyway.. you'll have to add another 23'000+ USD to the basic price for an RS6...