While technically true, high powered Solid state amps Like the JC1 do just fine to 105 dB (as high as I have gone) for several reasons. The JC1s due to a programming error I made absolutely fried the high frequency brilliance control and I mean barbequed BLACK and I had no idea this was happening until I smelled smoke. The JC1s merrily baked along without so much as a whimper. Tough amps.There is a reason Sound Lab made the B1 subwoofer, which was the size of the A1s they made at the time (back in the 1990s). But the use of subs isn't something limited to Sound Labs- many speakers benefit from not having lots of excursion.
Next, while the Soundlabs are capable of making plenty of bass the long excursions required below 100 Hz doppler distort everything else the speaker does. I am of the firm belief, know it for an absolute fact, that full range ESLs sound even better, much better, if you use them with subwoofers.
You have confirmed my comment- in order to work with Sound Labs your solid state amplifier needs to be high power. Since the impedance of almost any ESL varies by about 9;1 to 10:1 from the bass to 20KHz, quite often the solid state amp is making far too much power at 20KHz (A high power amp can probably double power as impedance is halved, but ESLs don't work that way, they need the same power regardless of impedance at a particular frequency in order to make the same sound pressure). Since you have to throttle it back somehow, the Brilliance control becomes a target as it has to dissipate some energy.
The trick of course is finding a solid state amp of that sort of power that simultaneously actually sounds like music (instead of like electronics); traditional class AB designs can be challenged in this area due to a lack of feedback at higher frequencies- which causes them to be bright and harsh (due to distortion) as I mentioned in my prior post. Its this particular problem which is why when distortion measurements are published, they are only measured at 100Hz. 1KHz and 10KHz distortion specs are usually not measured or published, but if they were you'd see that the distortion rises with frequency.
This lack is caused by inadequate Gain Bandwidth Product, which is engineering gobbledygook for "the amp runs out of feedback at higher frequencies". You can't just add more feedback- that takes more gain, part of that Gain Bandwidth product thing, and at some point all the frequency poles in the amp cause so much phase shift that at a certain frequency the feedback is positive rather than negative so the amp can oscillate. The engineering expression for this is 'the phase margin of the amp has been exceeded'. This is part of why the Brilliance control is so important on the Sound Lab when using solid state amps- you have to tone down both the excess energy and the brightness caused by distortion.