Yeah mate i'm fitting 20's to mine, Just make sure the offset is et35 (or can be made to et 35 with spacers)
And that the wheel is not any wider than 8.5 inches on the front, cos any wider and it hits the ****** strut which they made too close to the wheel!
You may be able to get 9 inch wide rims on the front at a squeeze but with 20's 8.5" wide on the front is the max for standard arches.
I've found this out having bought a set of 9.5x20 wheels! too wide!
they just won't go on a normal a6, but the will go on rs4's and rs6's
Hope this helps