A JPAC is for hooking up to the JAMMA harness. A monitor does not receive its power through the JAMMA harness, so your question doesn't apply.
Speakers don't require power. So again, your question doesn't apply.
The JPAC supports everything you need for quick and easy connection of all inputs, RGB+sync output, plus a few extras.
If you have a JAMMA cabinet that already works, then you DO NOT need to do anything other than add a PC, preferably with an ArcadeVGA card, and to be safe, cut off the power to the original power supply. NOTE, I said power supply. Don't confuse the ISOLATION TRANSFORMER as being a power supply. Chances are your monitor gets power from the isolation transformer (big heavy block thing).