I have built what I believe is probably the worlds cutest amp head switcher. The enclosure is a 30 year old lunch box... It switches between two heads on the same speaker cabinet, keeping the unused head connected to an 8ohm dummy load. I use permanent 220ohm 10W resistors across each jack coming from the amp head speaker outputs. This secures the amp against running with no load on the OT. The unit sits on top of the amps and is of course footswitchable. It is a bit messy inside at the moment, but that will hopefully change as time goes by. I haven't yet secured the two relays to the box, so they are kind of floating around on the inside.