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

@miller Thank you for this answer. I have a better sense now of why you made your first comment, and perhaps I let my feathers get ruffled too easily.

The cumulative voices against the switch are mounting, and I didn't intend for it to *replace* deep and patient listening; I meant for it to be an *additional* avenue of comparison. Wanted to make that clear. 

One detail of your story reminded me of my initial cause for posting:

 I had driven 200 miles. Okay I will try without the magic switch. Listened a few minutes to their wire. Okay, pause, put mine in. Instantly, and I mean so fast I hadn't time to sit down, it sounded like I broke the guys expensive tube amp. I could hardly believe. My wife was there too and she could hardly believe it herself.

Because I don't want to damage my tube amps, I don't have a chance to do what was part of your own story -- the fast switch, "so fast I hadn't had time to sit down." I'm not going to do that with my amp, so I have to hope that switching slowly is sufficient to hear all the differences I need to hear. And you -- and others -- have attested to that. So, that's what I'll do.

@teo_audio Thanks for this sensible comment, which echoes others:

If you find that you can’t tell the differences between the two, unless you had a switcher for instantaneous switching, then they are close sounding to one another.... close enough that it’s in the ’six of one, half dozen of the other’ kind of category.

I have only experienced a switcher in a store.

My general concern with "A" vs "B" comparisons is when listening to music our brains can 'color' the sound by adding memories to the equation.  Therefore, I've been more inclined to be introspective on what I hear and how I feel during the listening.  

And in the end I believe most of us like listening to music so I am comfortable with my decision being my decision because I'm sure that with enough time and effort I could realize my decision was merely good versus the 'best'.

In other words, enjoy your process!

I have more or less accepted the answer that "quick switching" is not the way to go.
By accident, I heard this said this morning by Hans Beekhuyzen — don't switch quickly to evaluate speakers.
https://youtu.be/idxT7VVYyxo?t=523 

What about switching between amps driving a single speaker?  I use an Ayre VX-5 Twenty stereo amp to drive KEF Reference 1s, but would like be able to switch easily to Cary single-ended monoblocks on occasion.  Any recommended switches for that?