Frankly, I don't listen very often at low volume levels, but my Sachs' amp seems to have no limitations in terms of listening volumes. A decade ago, Don upgraded my HK Citation II and V amps to a very fine degree, but his own amp is vastly better than either of them, by far.
I am aware that Clayton powers his speakers at shows with LTA amps, as I recall mostly the 11-wpc LTA integrated amp, which I heard at Axpona last year. I have heard the same LTA integrated driving his new M5 Sapphires and while I think his speakers are fantastic, I disagree that an 11-wpc amp, ss or tube, will properly drive his speakers. In fact, the fellow who auditioned the Sapphires for me has upgraded from his LTA unit to a pricey VAC Sigma 170i with 85 wpc channel and I understand that they really make the speakers reveal all their magic. The LTA integrated amp ought to perform well with Klipsch, Zu's, Omegas etc. but I would pass on them for Spatial Audio speakers.
I think the LTA is tonally a very pure amp, but it doesn't have the power to extract the full measure of Clayton's speakers.