Rikki,
Yes I think the p121 will MIDI fine to the SX....to use as a keybed...but of course not to fully control the SX900.
Lee
Yes that’s the dilemma I have, I don’t like stacking keyboards, , so controls would be a problem. Probably easier for organ players who are used to 2 sets of keys. The chord. Looper might come in handy.