Have you ever used a separate speaker selector unit to audition speakers? Would you?

@b_limo Thanks for giving a reason and not just an opinion.
@tablejockey I've been instructed not to turn tube amps off and then immediately back on but to give them a couple minutes. Folks have reported burning out rectifiers doing this.

You are correct about the amps.  Five minutes at minimum is a good starting point.  

@hilde45  "I have a tube amp that requires shut down, short break, between speaker changes"

@tablejockey "What is the reason for the shut down?"

OP runs tube amps.  Not a good idea to hot-disconnect and operate a valve/tube amplifier without a load. Without a load on the secondary, the output transformer primary presents a high impedance load to the output tubes, resulting in higher-than-normal voltages that can damage the tubes and/or transformer. Damage is likely if you operate the amplifier with a large input signal but no load. Might get away with it if there is no input signal and not recommended for most tube amps.  

Yeah. Don't.

Nonsense. Or maybe true if you are using a cheap switch. Niles, anyone?

A good selector switch is really a set of time adjusted relays that have little or no effect on the signal pass through them. I own and have used a Luxman AS-50R selector w/ remote for years and cannot hear it in the system. Proper placement and wiring is crucial. I think I paid just under $200 plus shipping from Japan on eBay several years ago.

Luxman makes several models, all good, but it's a lot easier and less disruptive to switch from your listening position. Van Alstine also makes a very good unit (ABX Switch Comparator).

These two companies also make good unbalanced (RCA) line level switch boxes. And Manley is making the Skipjack line level switch again, as I recall.

Look, no one would put a switch box in the signal path for no reason. But if you need to compare gear it's a much better way than powering up and down and swapping cables.

Look, no one would put a switch box in the signal path for no reason. But if you need to compare gear it’s a much better way than powering up and down and swapping cables.

This is the only reason I would put a switch box in -- to try to make a comparison. Then, I’d set it aside. Regarding @b_limo point about variables — the idea would be to use the same cable and keep the other elements as similar as possible (positioning, room, etc.) It might be necessary to quickly move the speaker being auditioned around a bit — but that can be quickly done, compared to the amp on and off rigamarole.

Of course, if the switch box isn’t high quality, then I could be degrading the sound too much for both speakers and erasing important details which would be crucial to their character — and their difference.

It seems this is another debate that rests upon empirical details not fully definite -- which speakers, which switch box, etc. I don't have the speakers yet, so this is impossible to detail, yet. I'm trying to decide on buying a switch box.

Another option is for me to get a switch box and try both. If I hear no degradation of sound with the switch box on either speaker, I can go ahead and compare them.