Since I am a 2 day old 1st Jamma cab owner, please take my guess with a grain of salt.
From what I have been reading, the buttons 1-4 should be already wired up to the Jamma Harness. This funcitonality will be carried through the JPAC to the PS2/USB already.
Since the Jamma harness can only supports the 4 buttons, the extra 2 buttons have to be wired directly to the JPAC to be sent to the PC.
I think this post was more for my knowledge than anybody elses

. Can someone confirm this for Gique and I?