IIRC,
AT PSU has a toggle switch, meaning it's always ON or always OFF, no momentary business. If that's true you could turn the AT power supply ON and connect it to a "smart strip" that is connected to your cabinet's PC, then it would turn on and off with the PC.
As for "eliminate some wires" - simply cut the wires off that you aren't using. (probably all but 2)
What is the AT PSU being used for?