Hi Ted,
The top row of pistons contains general pistons plus sequencer back, floating keyboard controls and a group of 10 plus zero matching the divisionals on the lower keyboards. Originally I planned for five manuals, but after deleting the fifth manual I kept its piston rail, positioned above the Solo after the fashion of many English cathedral organs.
Here is the final layout.
This scheme has developed over nearly four years. Originally I had no launchpads, and the rationale behind such a large number of pistons derives from the fact that I find touch screens extremely hard to use when playing. Even though I have since added launchpads to the console I have retained and refined the piston layout.
Andrew