Even with the RA module on the flat top of my Clavinova CLP-300, the controls were not very ergonomically ideal...everything had to be, and was, controlled by my left hand (except start/stop)...I couldn't put the module in the center, because of my music stand...

And, even though the buttons on the RA module weren't that far away, they had nowhere near the accessibility afforded by the buttons being on the keyboard/controller itself, and spread out to allow use by both hands.

I think you would need a dedicated, and specially designed controller to work with a module....and, thereby basically defeating the purpose of having the latter in the first place.

May as well just buy the arranger itself.

Sure, you can assign some functions to a foot-switch, but that's only a band-aid solution, and some of us don't want more pedals to deal with.

Just thinking out loud.