mystrodo

Be careful what wheels you put on a heavy Audi A6, it can change all the dynamics. OEM wheels are Forged Wheels, hence the reason they cost so much..Audi's testing and reasoning for putting Forged instead of cheaper Cast wheels are for spirited driving because of their strength plus they are also lighter wheels but also if you travel on pot holed roads you'll be glad you had the best wheels.
Changing any part of an Audi chassis including wheels needs serious thought IMO..there are many non-oem Audi wheels out there..check the list of sponsers here since they specialize in Audi but remember.. the strongest wheels are usually the ones that came on the car in Audi's case.
As to fitment..call the dealer for correct fitment numbers.

Zander

What springs and shocks you running? What you doing about alignment?

Audi-Freak

It's a K.A.W. PlusKit (springs + shocks), in front ~ 2,2" and rear 1,5" lower. The alignment is afaik original. In Germany you have to correct the wheel track and maybe the alignment in a workshop, before you are allowed to drive on public road. So I can't say in details, what was corrected, cause this made the guys in the workshop. But these settings apply only to the chassis and are independent of the wheels. It had nothing special to be changed for these rims.