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

I have the Adcom. It allows 3 pairs of speakers to be switched from one amp. 

For convenience, absolutely.

For differences that are so subtle / minor, yes...as I believe time and memory are not always on friendly terms.

For retail or industry reasons, yes.

Etc.

I believe learning to ’hear’ ’listen’ with greater accuracy and differentiation is valuable and worthwhile (both as pursuit and goal) and has been incredibly rewarding for me. Working on this has helped me dig much deeper into our hobby, understand it better, and has made it much more enjoyable.

If the box helps you do that, go for it...push yourself to make it more than simply a tool to compare speakers.

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

What is the reason for the shut down?

The reason is he doesn't want to fry his amp which is what will happen disconnecting speakers with it turned on.


Meanwhile....   

Anyone concerned about not being able to compare or judge because they will forget what they heard in a few minutes should stop and think about that. Ask yourself, if you really can't remember, then why would you care? If you have no memory of something better, how can anything be worse? Seriously. Think it through. Why would you care? 

Look at it another way. If the difference isn't big enough to be sure, how could it possibly be worth paying for? Might as well buy the pretty ones. Which if you can't remember, probably what you're gonna do anyway. So why bother?

Anyone concerned about not being able to compare or judge because they will forget what they heard in a few minutes should stop and think about that. Ask yourself, if you really can't remember, then why would you care?

That isn't the issue, the problem is you have no music in the hour(s) that wait for the tube amp to cool down and warm up.
A high quantity speaker A/B switcher is the solution, but you have to make sure the tube amp output is connected to a load at all time while power on.
A safe way to swap is mute the input, if the switcher is on speaker A, select A+B first then change to speaker B, so the tube amp will be loaded while swapping speakers.

@miller My effort to find a way to do careful and detailed analyses of complex phenomena does not stem from my inability to "think it through." Rather than imply I'm being obtuse, you could either just report that *you* never needed to do or perhaps suggest ways that you compare things.

Ask yourself, if you really can't remember, then why would you care? If you have no memory of something better, how can anything be worse? Seriously. Think it through. Why would you care?

Yes, one possibility here is that I'm just stupid. But another is that you tend to rush through experiences or don't pay enough attention to realize they are complex. To a gourmand, all food can be gobbled up quickly. But I've read other comments you've made in other places and know that you are a careful listener. Why not draw on that experience and contribute something you've learned to this topic rather than finding a way to demean the question -- and the questioner?