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

in most cases, for most people, sonic memory is good enough, long enough... so that no switching device is required.

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 submit that your ears, and recall... are very very likely to be good enough so that there is never any switcher required to get this sort of decision off the ground, after a few back-and-forths....

In many hundreds of speaker comparisons, I’ve never felt a need to arise for a switch-box. As 99.99% (of course that is an exact percentage! right...) of all ’different models and brands’ of speakers are so different, so obviously different, that no switcher could ever be of any fundamental use.

If I was tuning crossovers as a comparison to the original lab calibration sample speaker... THEN a switcher would be... quite possibly... critical. But then, burn in of the production sample vs the lab sample rears it’s head and you’ve got a difference and a mess again.

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?

Pretty sure you meant to say glutton. A gourmand will take his time because he enjoys eating. Gluttons gobble. Gourmonds savor. Just a little too much is all. 

All you have done is buy into the same evanescent memory trap as so many others. Its easy to do- at a keyboard. The minute you step away from the keyboard, and actually go and listen, that is when you learn what is what. Once you do it blows the blather away in an instant. 

Like if you read back far enough in my posts this will be about the third or fourth time relating this, the story of back when I believed the evanescent memory blather. I drove 200 miles to where they had just the magic switch you seek. Because surely whatever slight difference there might be between interconnects had to be so miniscule no one could possibly be sure or remember unless switching back and forth fast and often. 

When I got there the magic switch was broken. 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. 

There's a million things to say about how to listen. But really its not how to listen, you already do that just fine yourself. Everyone does. Only reason we're here is a million ancestors heard the twig snap and froze or hid or ran or fought. But they heard the twig snap. So you hear just fine. What you need is the language to understand and describe what you are hearing. This you only learn by actually taking the time to listen and compare. Which sad to say cannot be done at a keyboard. 

The differences between interconnects are obvious and easy to hear. The differences between speakers are obvious and easy to hear on steroids. 

Go and listen. You will see. 

@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!