Steve - that arpeggiator idea is just the sort of thing that would be nice to try out if I can get this to work.
Indeed I have seen that the manual shows that it responds to local off, I simply don't know how to go about sending that control change message. This isn't really an issue of the CZ itself at this point, rather a question of how to communicate with it.
As you advise "turn it off on your basic channel with a control change and see if notes don't reach the synth engine from the keypresses" - that is exactly what I am trying to achieve, I just don't know how to do it.