The RS6 Drilled and non-drilled rotor part #'s are:
front cross drilled rotor
4B3 615 301 E
4B3 615 302 A

front non cross drilled rotor
4B3 615 301 B
4B3 615 302

rear cross drilled rotor
4B3 615 601 C
4B3 615 602 A

rear non cross drilled rotor
4B3 615 601 B
4B3 615 602

P.S. here is a thread that talks about those discs:
http://audisrs.com/archive/replaceme...t__t_1572.html