You’re probably feeling the stiffer suspension of the S6 - nothing to worry about. the stiffer your suspension, the less travel you have, making bumps "launch" the car more than usual. The S6's suspension is quite a bit stiffer than the regular A6 suspension. i wouldn’t worry... I suppose if you didn’t like the stiffness you could change the springs out with some from an A6 avant 4.2 but... i don’t know why you would :huh:
as far as performance mods - read the first post in this thread... APR makes great chips, i'm not quite sure if they make on for the S6. MTM also makes an awesome chip.. and I know they have one for your application. Whats good about a chip in a non-turbo car is the dealer will usually not void the warranty because the engine isnt under that much added stress. Look for about 15-20hp out of a good chip.
The shift points on the S6 are pretty bad – you have two options to correct this. You can modify the computer system to support higher shift points, as well as make the steering wheel buttons work all the time (even in normal drive). This is called a VAG-COM 00032 modification.
You can also look into a tiptronic chip, which will raise the shift points and give you a bit faster shifts. You may want to note that this WILL void your transmission warranty.
The manifold is about the best out there and doesn’t really need to be changed unless you’re really looking to fly. If you’re going thru all the trouble of changing the manifold, you might as well throw a turbo or two into the mix as well.
Somewhere in all that mess, you should throw a K&N filter in and sway bars… Wheels/Tires should be changed at some point, and a break kit should be added with all this extra h/p.