Ted Weber used to sell an amp switcher that would switch multiple amps on the outputs safely to a load or a speaker. It was called the Four head and it could switch 4 at a time. I have the last one made before they discontinued it. They still make a switcher but I think it only does two amps at a time. I never opened the Four Head up to see what it was doing internally., but it does work well.
Greg
DIY amp head switcher
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