Amp's nominal power rating - any use?

Magfan, the phase angle discussion you're trying to have is frequency-dependent, which you've ignored, so "next to nothing" still seems a stretch to me, which was my point. Since most listening, even on the OP's speakers, will be done with the first few watts, the effective frequency response will be the most important determinator of the sound.

Couple of points....and some agreement.
Yes, phase and impedance ARE frequency dependent.
I think the main take-away would be that a large phase angle coupled with an impedance dip is an amp stresser....(is that a word?)

Also.....and I don't remember which, Tube amps simply do not like a very reactive load. Capacitive? Inductive? don't 'memeber which.
Their is a good reason for this to do with transformers, right?

I don't believe 'next to nothing' is a fair characterization. Given that the PAIRING is a most important aspect to choosing amp/speaker combos, you can't simply ignore phase/impedance characteristics of the load and the amps response TO such loads.

Overcome a 'weird load' with simply more amplifier power? A solution, of sorts. I've heard talk of 'cheap watts' which is one answer. Another approach is the rational design of speakers.... We've all heard of some of the wacky stuff out there which apparently need something from Lincoln or Miller to drive.
I'll leave that decision up to YOU!

Now, about a proposed amp test? I think I'd like to see some data before I simply tossed that out. A resistor may be a nice, standard way to test an amp, but has little or nothing to do with real world conditions. Even my panels have reactive elements, though the impedance curve is pretty flat with only a rise at the crossover frequency. I'd love to see amps tested for power with real world reactive loading. A simulated speaker load could be agreed upon. The worst loading should be below....say 1khz, where most of the amps power goes, anyway, in real music.

And as for the OP's speakers. Fine stuff. Pricey and apparently worth it to some. I can't possibly criticize that choice. But, I would caution the owner to look at the pairing amp carefully. A large phase angle load, regardless of impedance, will still eat into amp power. Large impedance swings also, IMO, kind of defeat the purpose of tube amps. The more recent stereophile test of the similar SF speaker says you may want to use the 4 ohm taps, even though a straight look at the impedance curve may indicate the8 ohm taps.
If I wanted tubes with that speaker, I'd for sure try both.
The OLD test by stereophile did not measure such phase data. The new test indicates moderate phase and impedance curves....probably not a bad load for tube OR SS..

Perhaps it's a starting point without direction?

Dongiovanni, I confess to being biased against SET amps. I think most people that like them are just hearing a modified frequency response caused by the electrical anomalies of the output stage, like a high output impedance. Frankly, considering the high quality of your speakers, I think it might be very interesting if you try a solid-state amp and tell us what you think. If the receiver is good enough (they do okay above approximately the $500 price point) you will at least get a first impression, though the speakers are good enough a better amp might have an audible difference. If you still think the SET amp sounds a lot better, I respect that. Choosing a system is personal decision.

The issue with power ratings is that there are so many variables, and many ways to test power output. It also takes ten times the power to increase the volume by ten db. If you are happy with what you have, and it's only a matter of worrying about the wattage specifications not aligning up, don't worry about it. As long as the amp can get loud enough without clipping, which sounds bad, you are good to go.