Quoted from Rondogg:

Just curious if anyone has cleared up the hum by adding a Pinsound board on its own...

Quoted from wayout440:

This is the only solution so far that has produced favorable results. Not floating the sound board, not replacing caps, not disconnecting braided grounds on speakers. Running the sound board off a separate supply reduces noise dramatically. I assume this is mostly because of the replacement supply has a much cleaner regulated DC power, as well as eliminating ground loop. I used an open frame Artesyn supply. It's 40W and has no fan, we used it in some of our older pro audio products.
I just have to mount it permanently, I'll try to get pics once it's done.

Quoted from wayout440:

Yes, you want to join after the power switch no matter what pin you are wiring up with. This goes for any accessory, mod, or powered subwoofer so that the device comes on when the master power switch is turned on. What you are looking for is the transformer primary side wire pair (usually a black and white wire colored pair) that runs from the power switch to the main transformer. In most games, the mains switch is in a metal enclosure. I prefer to make the tap connections within the box if present. Cut the wires cleanly about 4" away to give yourself some room, strip and connect all three black and all three white with wire nuts (diagram shows just black wire connection, do the same also for the white) PLEASE MAKE SURE YOUR GAME IS UNPLUGGED for safety before you tap into power, regardless if you believe the mains switch is off.
Notice also, according to the schematics for Maverick, the bill validator connection is also a viable option if not using a bill validator. To use it, all you would need is build a proper connector for your accessory.

Quoted from wayout440:

No problem. I'm not going to include the power supply side, because that could vary with the model you install. A datasheet should be included with it. For the sound board side you'll need 4 connections. I know it is the same for Maverick and Guns n Roses. Double check your own schematics for other DE games. I advise to be consistent with wire colors that are fairly standard for audio power, if possible. black=ground, red= +5VDC, orange= +12VDC and grey= -12VDC