Thanks this is what I suspected. I have a midi sax (Yamaha WX5), which sends monophonic midi, but is really expressive. Kind of hoped it would be able play the chords set up in the progression But also as Inbushis suggest, have chords triggered on a range of the keyboard whilst playing extension and melodies in another.
I have a midi vst plugin which is great for this. This guy is the master, everything you hear is being played from one not at a time (not that I'm hoping to do the same, that would require 4 MPC Ones)