@prrjim, I'm curious; is your friend only running MTH engines with PS3 electronics? If so, there may be no "functional" differences, but "feature-wise" he has a somewhat limited (less than the entire universe) pool of locomotives to run. If your friend is running other 3-rail (non-PS3) MTH engines, Lionel engines, Atlas engines, etc., didn't he have to modify the engine electronics and/or motor to install DCC in those engines?
Chuck