High Sensitivity Speakers that work best with SS

I think that most speakers, high efficiency or not, sound better with good tube amps than solid state, provided the amps are not pushed very hard. But, with many low efficiency speakers it really is hard to run them in a low-powered amps sweet spot if one listens at fairly high volume. I personally don't like most high-powered tetrode and pentode amps, the exception being OTL amps.

High efficiency speakers allow one to better exploit the advantages of tube gear, but, they can make the best of solid state gear as well.

I have heard my system with the First Watt J2 amp and I liked that amp a lot. The J2 delivers clarity, natural timbre and a grain-free sound. It does not quite deliver the enveloping soundstage of a good SET amp and notes don't quite give the impression of blooming into space and decaying naturally like a SET amp, but, the J2 is still good in this regard. The slightly hard edge to the initial attack of notes gives it away as a solid state amp. Still, I think it is a VERY good amp, particularly considering the price. I wish there was some way to hear their SIT amp in my system (the friend who bought the J2 and lent it to me for a week is not likely to buy another First Watt amp).

Is it possible that high powered amps delivering 1 watt will sound worse than a lower powered amp delivering that watt? I would hazard to guess that the answer is yes. I've heard a few demonstrations of high powered amps vs. low powered amps from the same manufacturer, and often, the lower powered version sounded better where high power was not needed. Sure, a whole lot of other factors are not controlled and the design and components, etc. could be radically different between the two amps, so I am not drawing any hard conclusions. I know some solid state designers have gone to almost heroic extremes to minimize the number of output devices in their design because they claim that paralleling multiple devices degrade the sound. I have no idea if this is true, but, at least this is a plausible explanation of why some don't like the sound of high powered amps on high efficiency speakers.

As for the issue of high efficiency speakers that are difficult loads, I have found that compatibility with tube gear IS very much related to the difficulty of the load. A speaker, like some of the Wilson speakers, are surprisingly efficient (mid 90s), but none sound very good with most tube gear because they are difficult to drive. Other much less efficient speakers, e.g., Spendors, are MUCH more compatible with low-powered tube amps. I recently heard an old BBC monitor speaker (mid 80s efficiency rating, a 15 ohm nominal impedance) used with some quite low-powered pushpull amps (5 watts or so) and the combination sounded fantastic.