You'll have to chase down the wiring harness to figure out what goes where. It doesn't look like that unit has a seperate audio amplifier, which is part of the problem.
You'll need to wire in a seperate amplifier, be it a Car unit with an external PSU, or a home unit. Run your JAMMA harness audio lines to the amplifier (you'll probably need to make your own adapters) and take the amplified outputs and run those to your speakers (this is why you'll be chasing the wiring around).
Probably ~1hr worth of work, tops.