Uneven soundstage help, please.

distance from the listening spot to the right and left speakers is identical, same degree of toe in for left and right speakers, speakers are level and the same height?

This! ^^

Foolproof method in oddball rooms, what I have done before including at CES so I know it works:
Pull a string to establish a straight line between the two speakers. Use a framing square to go straight off mid-line to your listening chair. This establishes your perfectly equidistant and symmetrical speaker/listener triangle. Proceed to tweak to find the right amount of toe in. This is Step One.

Step Two, listen and look. Asymmetrical room reflections will pull and smear imaging. How and how much, and what sounds it affects, all depends on the various room surfaces. So look around. Follow lines of radiation patterns

Yes it will sound a lot better if this is resolved. Because right now you're noticing the obvious effects. If you are able to correct them however then you will notice a lot of less obvious effects are also gone.

You mention the wife factor. There's some guys, and I use the term guys loosely in this case, who were triggered when I said we do things to please women. Apparently we are all such rugged individualists we never turn our lives inside out to please the dames. Or if we do we're too ruggedly stoic to talk about it. So probably you misspoke. But if you do all this alignment stuff and still want better imaging without upsetting you know who too much Synergistic Research makes these little wonders called HFT which she who doesn't factor in will probably not even notice if you put them on your speakers. 

Seriously. They totally work.

Well, to completely understand, you can’t move the speakers, and you can’t add better room acoustic treatments, like GIK Art panels which let you pick any artwork and put it on them.

Those are always my first two suggestions. You can try crossing your speakers in front of your head, minimizing side reflections.

Lastly, if none of this work it's probably becuase you are getting a very unbalanced frequency response.  Assuming it's not bad speakers, you will need to measure and adjust using EQ, either from a separate unit, or by using the built in EQ of Roon or similar. If you aren’t familiar with measurement and correction I suggest you get something that has room correction built in, like Anthem pre/receivers, etc. or a miniDSP unit with Dirac live built in.

Here's an example of how I corrected a much milder problem than you are having using the built in EQ from Roon:

https://speakermakersjourney.blogspot.com/2020/01/the-snr-1-room-response-and-roon.html

What you should do is pick a speaker with the least reflections around it as your baseline, and try to get your other speaker to match it.

If you use ARC, like Dirac or Anthem they will do it all for you.

Thanks for great suggestions. More details: it's not the amp--no problem with different speakers. Equilateral distances and height and rear wall distance all the same. One rear wall is a thin layer of veneered plywood, the other is plywood backed by the metal frame of a large oven. I have one speaker toed-in more than the other, which helps vs hinders the problem That one is facing a wall of angled picture windows across a shorter distance than the other one. which faces more complex, longer angles. The high ceiling above them is slanted differentially too. I could hardly draw a room map, it's so complex.
My source(s) are the same as before when I had my old speakers-- the weak spot in my chain. But why would they suddenly worsen the moment I set up the ATCs? And I totally trust the wonderful guy I bought the speakers from. They worked impeccably in his system.
The volume from speaker to speaker is consistent. It feels like a romm/placement deal.
Of course I'll check out all the things y'all have mentioned, as well as the products/devices.
It definitely could be my ears. I'm 68 and I know I hear a bit better in one ear than the other. It didn't occur to me that this could affect soundstage. It's just something i'm used to.
I'll check connections. I did have trouble with one of the terminals on one of the speakers originally, It was very fussy.
I can't help thinking it's at least partially things about my room that are more unfriendly to the newer speakers. They're closed boxes and the KEFs were rear ported. Maybe this makes a difference? I would think it would help with a difficult room. Any more simple placement ideas? Maybe something counterintuitive?

I just tried sitting backwards. Bingo!
What can I do if it's my ears?