I am not sure why there is a "sudden" interest in SOA protection in numerous threads at the moment. Haven't we DIYers (not professional Electrical Engineers) known about this forever and deliberately decided to accept the risks?
Can those relays be used to turn off the supply rails instead of having them in series with the output?
In other words, if SOA protection is invoked or DC offset detected, then disconnect the DC supplies from the amplifier.
A latch would be necessary as you don't want the supply rails re-connected to the amplifier unless power is cycled.
Yes, you could switch the rails - in fact it would probably be easier than the speaker. I have toyed with the idea but not organized my thoughts into a circuit yet.
There seems to have been a profusion of protection circuits lately - driven I believe by fast MOSFET switches, cheap bipolar output transistors and more use of simulators.
You can take a look at my circuit diagram and, maybe take some ideas from it(as I took some from JLH)