Are you talking about an A/B that routes which sound module is going to your amplifier? That's the only thing you could be referinng to, but why spend for that when you don't have to? Then, furthermore, that would be a hindrance to you when you did in fact want both sound modules playing at the same time. You would then have to disconnect the A/B and wire both sound modules to the amplifier directly when you want to hear both at the same time. What a headache.
Best thing is to have separate audio cables from both your Roland and Korg going to your amplifier, and leave your Roland off until your ready to hear it.
Both of these instruments you own have channel routing built into them, so you just need to learn your software menus in each. The point is, you can have everything physically "ON" but if the channel routing is turned off on one of the instruments, you have accomplished what you want. No need to use an A/B switch.
It's kinda like your car is on and running, but you don't push the cigarette lighter in until you need it. It's always available. Same thing with your trunk release. It's always "on", but it does not function until you push the switch.
You probably can turn a knob on one of those instruments, thus disengaging it from the Loop, when you don't want to hear it, without literally turning the instrument off.
