Best tube amp for electrostatic speakers

Atmasphere, thanks, that was the kind of education that I needed. I've spent 55+ yrs in this hobby but have never been a student of it and is now why I'm having to ask so many questions. Regarding the ESL impedance curve, if I'm understanding the explanation, the impedance effects of my newer Ethos speakers should be somewhat less significant than the Odysseys that they replaced because of their smaller size and the more limited lower range capability of the panels. It seems to me, then, that my issues with upper frequencies should be somewhat reduced using these smaller panels. However, that doesn't seem to be the case.

A question I have regarding your discussion of feedback is that if it results in an increase in upper level harmonics, would that not also enhance perception of timbre?
For some time now I've suspected that there is some sort of antagonistic relationship between timbre and brightness and, because the timbre issue is one of the most important issues to me and brightness is my least acceptable, I seem always to be walking a tightrope between the two. Of course, my perceptions and ultimate conclusions regarding this interpretation could be way off base.

Your explanations, at least to the extent that I think I understand ithem, make a great deal of sense and I hope that my comments do them no injustice. It will, though, take some time for me to digest and expand on them before I comment further.
My first choice would be Carver Lightning, than I'd look for Manley or VTL amps 200+wpc. They're stable to 2Ohm impedance. Also semi-professional tube amp Mesa Baron handles tough impedance curves very well.
I have only a rudimentary understanding of impedance matching, effects of Ohms, etc. However, I have real world experience with my particular set of tube amps and have been researching if an upgrade is available for my application w/ ESL speakers.

I have a set of Dennis Had designed SixPac mono blocks. They are 50w/ch triodes and I am running a pair of 4ohm min impedance 87db ESL speakers which shouldn't be a great match. At very high SPL I run out of amplifier, but only at 95db+. My wife finds this combination "very smooth...not bright or fatiguing at all...."

As I have been researching amp upgrades I was considering the Manley and Rogue. The Manley was recommended only if I wanted a "brighter" more solid state sound. The Rogue were recommended as a good clean sounding upgrade, but these too may be brighter than my preference.

As I looked further I found that Dennis Had designed the Cary V12 with a very similar circuit to the SixPac only allowing for triode/ultralinear switchability. This seems to be ideal as you could have both power and sound options depending on your listening. It seems that V12 amps are available periodically for a reasonable used price. It's just my .02 worth and wholly unscientific, but might be worth a try.

Lastly, I had considered the Mcintosh MC275. That amp will provide good output and have less "timbre" and brightness. They would also be an easy amp for you to audition as I think most Mac dealers have them available for trial.

Good luck.