Hello all, new question, multiple jamma controllers/multiple boards

[mr aize]

Right, i've decided to try and build a cab but since i don't have a lot of space, i'm going to build a bar top, single player one... However, i'm thinking of adding a few outputs/inputs for some extra options..
I've decided against building a mame cabinet, simply because I already own a neo geo mvs board and am hopefully getting a cps2...
Firstly, i plan to put an extra dsub socket for a second controller, all simple so far, but because space will be a problem, i'm thinking of adding a fully wired scart socket in the back, which will allow me to feed a separate tv at the same time so player 2 can play in front of their own tv, using a controller.
Secondly, i'm thinking of adding another dsub which will be looped over from the controls in the cab. The idea behind this, is that i'm going to put in two power switches, one for the monitor and one for the board. This is so that I can power up just the monitor and, using a separate lead, connect the controls of the cab to my supergun or megadrive (already built an adapter) and play them through the cab. My question then, is would the fact that the controls are powered up via the supergun/megadrive, but not the board, cause any potential problems, damage any components or simply not work? Afraid my electronics knowledge is limited to soldering a few components together so thought i'd ask here. Thanks in advance

[mr aize]

Bump... Anyone? In case my rambling question isn't clear, i'll try an explain more. Basically, i want to build a cab with a jamma set up and a cps2 board permanently hooked up inside it. I then want to add a dsub 15 pin outlet (looped over from the controls) and a scart plug which will let me use the controls and monitor to play my other consoles (using various converters etc). What i'm wondering, is if megadrives/playstations etc use higher voltages than cps2 for the controllers? If so, could leaving the cps2 board connected potentially dammage it? Anyone know? Help please cos if it would, i'll have to modify my design a bit..