The manufacturer of this particular organ tells me that there is no MIDI information regarding the pistons and that they are not part of the MIDI set-up. However, when the add-on organ expander is connected, a little green light flashes not only when you press a key but also when you press a piston, indicating (says a more clued-up than we friend of ours) that there IS a midi channel in operation via the pistons.
SOMEWHERE on the internet, you can download for free a MIDI CHANNEL TRACER / MIDI CHANNEL FINDER / MIDI CHANNEL something-or-other to help us verify it
But where.............
Any MIDI buffs out there!!?