OKAY...I'll jump in.

I had been playing the new generation of Yamaha arrangers for several years before I discovered how to transpose SMF's, AND the KEYBOARD'S keys to the key signature I wanted to sing in. For instance, maybe the SMF needed to lowered 2 half steps, but the keys had to be raised to +3 in order to be coordinated.

The Transpose + and - buttons regulate transpose as a MASTER function. But, in order to transpose your MIDI FILE and THE KEYBOARD'S KEYS individually, first hit "DIRECT ACCESS", then the "TRANSPOSE +" button.

From there you can select MASTER, SONG (the SMF file) and KBD. Once all the keys are coordinated, it is just a matter of saving it all to a registration.

I can't speak for brands other than the Yamaha, but I'll bet most, if not all, of the newer arrangers offer this feature.

Eddie