Geoff did not read my earlier posts carefully enough, for my other speakers are no longer the LS3/5a (lent those to my son while he is saving for a pair of Harbeth M30.1’s) but the much better Harbeth P3ESRs.
As it so happens I once attended one of Peter Walker’s blind comparisons between his three amplifier designs. Those were the days when people began to claim that tubes sounded better, and he thought they were nuts. I subjected myself to the test rig, and did indeed think that I could hear differences. Peter was pleased no end when he could show me that I had been no better than completely random. And I learned a valuable lesson. The stricture is, of course, that amplifiers have to be designed properly. If you read the Stereophile test of his valve amplifier, you can see that Peter Walker’s own valve design does indeed perform quite well under a varyring speaker load (flat within 1dB):
https://www.stereophile.com/content/quad-ii-classic-monoblock-power-amplifier-measurements That is much better than many other valve amplifiers.
It is indeed a legendary design, just like his later 303 and the more powerful 405 current dumping model that still lives on in the again more powerful 606, 909, QSP and current Artera models. As Peter told me, the only practical difference is that of more power. Since at the time I was using the ELS57’s that could not handle more than my 303’s 45 watt per channel, he assured me there was no point in upgrading to the 405. A true gentleman.