I've wondered for some time if it is possible to use a multi jamma kit to have both PCB and MAME in the same cab without having to switch the JAMMA connector manually. I've asked ultimarc and the makers of the multi-jamma kit as well as posted here in the past and never really heard for sure if it was possiible.
Yes, the multijamma kit works with jamma games and a jpac. I asked that question along time ago. Might still have the email archived somewhere.
Anyway, back to the problem at hand. WHY?? It would be best, for 4 players, to got with a jpac and ipac. You'd have to custom program both most likely.
Anyway, your idea of having the ipac4 and optipac to the jpac (which theoptipac can't interface witht eh jpac anyway) would be a huge waste of money.
As suggested it would be best to just get an optipac, ipac2, and jpac. Or a minipac and jpac.
Now realize, only JAMMA games will hook up to the JPAC. JAMMA+ games will require some work but can be done with the jpac too. So what you are going to have is players 1 and 2 will hook up to the jpac, players 3 and 4 to the ipac2, the tball and spinner to the optipac. (tball, spinner, player 3 and 4 to the minipac if you go that route. I'd then suggest using the USB connection for this instead o daisy chaining through the ps/2 port.
Also you will need to hook up to an arcade monitor I'd assume if you start getting arcade PCBs. The best way to do that is the ArcadeVGA.