i think you could just use a 3pdt and wire it so the 1st pole is connected to the input tip, and the top trow is out to fxloop A's tip, bottom throw is out to fxloop B's tip, then the middle pole is to the out jack tip, and the top thrpw is A's return tip ,bottom throw is return B's tip...
just like a normal dpdt wiring... and you just use the third pole wired up like a channel switch with led... i think these type of 'universal channle switches are just a spst with a led to tell you when its on...or in this case when channel B is on...
--- third pole wired like the top 'to amp channel' part with the left circle representing the middle lug, and ground at either the top lug or bottom lug (or wired to a 'out of phase' type dpdt switch to change which loop gets a light... maybee with the addition of a dual color led you could get light for a when on as well as a different color for b? not sure ,but this way you can at least get one led for loop b/channel 2
and off (no light) for loop A / channel 1...
