Aroc, is that person your referring to me? If not, add another to the list.
I ran Sound-Lab Ultimate Ones for nearly two years with the original Viva 572 based amp (21 watts) and later the 845 version.
Indeed, the big Sound-Labs will produce acceptable levels with these amps, provided you are not concerned with sweeping dynamic contrast or loud passages.
I got excellent performance with Jazz, particularly small group and piano jazz trio. Also excellent with all female vocals. Sound pressure level with incredible emotion and textures, up to about 90 DB (12-14 feet), with the only issue being complex classical and Rock and Roll (sudden high amplitude material) that always stretched the power supply of that little SET facing the Sound-Lab load and trying to fill my large space.
There is indeed something special about the sound of a single driver speaker driven by a single output tube running class A. Purity that is addictive and makes you forget about the gear and listen to ONLY the music.
Besides, when it only plays that loud, everyone has to shut up and listen instead of trying to compete with the speakers.