Most excellent, dude! Now back to jammin'.Bingo!
So far the problem seems to be solved. The device responds to all buttons and to my midi foot controller.
A faulty Z80ADART IC was the problem.
I will surely eventually pick up a Triaxis as part of my quest to have the entire Mark Family lineup. Even if you want to call the Triaxis an island unto itself, it can't hide its Mark DNA.