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.
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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.