Thanks Burkhard,Hi Rastaman,
I f you want to toggle between your amps and not run both amps simultaneously you could use a Little Lehle. This Switcher switches apart from the signal also the grounds of both amps. Through this feature you can't get any hum-loop.
To ABY (Y- stands normally for both amps simultaneously) your amps you can use the Little Dual or the Dual SGoS which have both now a phase-reverse and a ground switches.
Only the old style Dual has a ground switch which is located inside the box. You have to open the top to switch it.
All the best