great post, I am doing almost the same thing with a Blitz/Showtime cabinet and plan on adding a Multi Jamma kit to plug in additional PCB boards... I like gauntlet legends etc (un emulated games).
its a very confusing process, especially the control panel.... I am going to have multiple controls-- 4 -8ways, spinner, trackball, flight stick, throttle stick, 2 rotary sticks.
I am not sure how this is all going to work with a Jpac and a Ipac 4 but it looks like you got most of it to work.
thanks
Scott
Detroit