Jay, your assessment is opposite of mine but I respect it, especially since my own opinion of ss-amp improvement was not based on direct comparison but only on my recollection and experience. It seems to me, however, that for about 20 years (late 70s to mid-90s), each time I replaced a ss amp in my system (Dynaco, Yamaha, Hafler, Adcom, GAS, PS audio, B & K, Threshold, Krell, Rowland Research), the new one was always a little better than its predecessor. After all, they incorporated new designs, such as zero feedback, class A, high current, extended bandwidth, MOSFET, JFET, stiff power supply, dual mono construction, balanced inputs, high-quality parts capacitors & resistors in critical areas, etc. So, I logically concluded that my current ss amps must be much better than the one I owned in the late 70s. I still believe that.
Out of curiosity, I dusted off my old Hafler (early 80s vintage) from my storage room and hooked it up to my current system. And the sound was…far worse than I remembered: grainy, dry, very Hi-fi and not musical at all. The focus and soundstage were particularly disappointing. Even my low-cost B & K ST120 (late 80s/early 90s) sounded significantly better in every respect except perhaps punch. I would not overstretch my recollection to say that any of the ss amps from the mid-80s to the mid-90s by Audio Research, Counterpoint, Krell, Mark Levinson, Rowland Research, Threshold, etc. would sound better than vintage ss amps from the late 70s to early 80s.
You mentioned Mr. Kloss, a man I greatly respect and admire, and his famous Advent speakers. What a coincidence. I dusted off m y AR 3a and Large Advent speakers—you guessed it! I never throw anything away—which were considered some of the best speakers in the late 70s and early 80s. I hooked them up to my current electronics. Their sound was…disappointing! The bass was deep but ponderous and muddy; the midrange was OK but not terribly dynamic; the top end was muffled, lacking in sparkles. As in the Hafler’s case, the overall sound of these speakers was Hi-fi rather than musical. I grant you that comparing these speakers to today’s better speakers was probably unfair. But even compared to my Celestion video speakers, the venerable AR and Advent sounded hopelessly outdated and outclassed. I would venture to say that many speakers from the 80s to mid-90s like the Magnapan II or III, Marti-Logan CLS, Vandersteen, Thiel, KEF, just to name those I am very familiar with, would easily outperform the vintage AR 3a and Large Advent. The parallel may be instructive though I am getting way off the topic of amplifier evolution. Sorry.