Well I'll be surprised if there aren't turbos on the C6 RS6 or the RS5...Because Audi have moved away in a different direction and gone N/A....... perhaps you missed the lack of turbos on the RS4 and R8?????
There is no way you'll get 580hp out of a 4.2 V8 or 5.0 V10 without turbos...unless it revs to 10K rpm...