All examples on the Controller/Pedal Switcher seem to indicate that only two amps can be A/B'd using Loop 4. Could you not loop, say two additional amps by sending via Loop 3 and Loop 2. Now, getting signal to more than one amp at the same time would require a splitter at one of these loop outs, but, also doable provided you have more than on Input for a given amp channel?
What am I missing? How could this go wrong? Thanks

The Send jacks can be used to have a switchable signal route, however only one can be active at any time. The possibility of ground loop buzz exists as the loops all share a common ground. I hope that helps!