These are all the same model software-wise, but the mounting is different.
DS-KD8003: the actual doorbell module with nothing else. Same as DS-KD8003-IME1. Needs a housing to install (with 1, 2 or 3 modules).
DS-KD8003-IME1/S: silver version of the doorbell.
DS-KD8003/Surface: Module with...