The newer RS4 Avant and the RS5 have bigger wave rotors for the rear and all you have to do is space the caliper to fit. But you need 19's at least.

There is also a bigger factory front rotor and you'll need 12mm-15mm caliper bolt spacers, but I've found it's much more cheaper to use the Girodisk rotors cost wise, and they're probably stronger for track use.