While I don't know much about either the MP-201 and the M9, I did take a quick look at both manuals--it looks like the expression pedal is CV only, and the M9 expression input only takes in expression pedal input. I didn't see anywhere that said the M9 takes in CV, and
AFAIK, CV isn't interchangeable with expression pedal signals...you'd need a converter or a different expression pedal