As a C5 owner this is not really my area but I'm guessing there's not much difference (other than the C5 didn't have XM!). You can probably install the factory setup at great expense, but why bother? Get a Roady 2 (or similar) and use the FM option, or search for wiring harnesses that connect to the factory wiring (avail for C5s, not sure about C6.) As for the antenna, roof mount won't work so look for posts on mounting inside the rear bumper; I've got mine mounted at the base of the windshield in the wiper tray - works fine.