from my understanding, the rears on the iS models are ventilated, and the fronts are bigger that regular, hence the requirement for 18" wheels minimum (even a spare is at 19")... the rears on the regular E53 are not ventilated, and the cross check in realoem does not match those rotors back to regular X...

i would say - no...

but, as always, you better check with somebody who knows this...