Heh, somehow I got this far without figuring out how to quit.
Here are the controls currently on my cabinet (available to windows):
Joy1
Joy2
Joy1 buttons 1-7 (controls + p1start)
Joy2 buttons 1-7 (controls + p2start)
Mouse1+2+3 (insert coin1+2, pause)
I'm sure I can bind a combo (likely joy1b7, joy2b7, mouse3) to quit in MAME. However, this won't work for most other emulators I wouldn't expect. I could shell out for a keyboard encoder like an IPAC and just wire a few keys to trigger Escape but that seems a little excessive. Is there another solution?
FWIW I'm tossing up between GameEx and MALA for my interface.