Sorry, my English play's tricks on me. I still don't understand what you mean with motor control, do you mean a real motor like the ones you got on a tape loader?
I don't know MSX, but for an ZX you would just need the functions to play/pause/stop the wav, maybe fast forward to find next levels, like outrun as example.
The MSX needs to pause the loader? Does it give the order to the loader, automatically? where the motor fit in this?