[mhennessy]

I have an Arcam Alpha 2, which uses the same power amplifier as the 3.

It has current limiting and "catch" diodes, as well as output fuses. I would have no concerns about using it "live" with a speaker switch. I routinely change speaker connections without powering down amplifiers, and have never had an issue. No competently designed amplifier should be bothered by sudden disconnection or accidental short circuit when silent or playing quietly. Remember; a just a couple of volts is a lot of noise given that speakers generally produce anywhere between 80 and 90dB when driven with 1 watt.

In the highly unlikely event that the Arcam does suffer, it's an easy amp to repair as it mostly uses transistors that are easy to source (TIP2955/3055, BC547, etc). The exceptions are the drivers, VAS and VAS current load, being FST239/240 and MPSA056, but it won't be impossible to find substitutes.

Obviously, I have this viewpoint because I'm able to do a repair if necessary, so the "consequence" part of the risk assessment (likelihood-times-consequence) is just a minor irritation for me. If you have to pay someone to repair an amplifier that fails, the consequence is higher. But as the "likelihood" side of the equation remains vanishingly small, it's still a very low risk, whatever your position.

It's worth saying that power-cycling amplifiers is not completely risk-free either...

And please don't wire speakers systems in series! Remember that the impedance varies wildly with frequency, so they won't sound anything like the designer intended. Parallel is fine. I used that Arcam to power a 4 ohm subwoofer for many years - it never complained.