How important is the efficiency of a speaker to you?

Usually low efficiency means complex crossovers. The issues of cross interference, phase coherence and latency resulting from multiple transducers compaerd to a two way, ideally point source in my mind are too complex to solve. That’s why flea amps with high efficiency speakers have such a strong following among true audiophiles

I'm happy with my bi-amped system which combines an efficient dipole line array (98db/w) driven by a DHT SET, and a dipole servo woofer tower handling the lower few octaves and driven by an 800w class D amp. This is the best of both worlds for me. Fast, tight, powerful bass and gorgeous, spacious mids and highs. 

When discussing speakers that are hard to drive, I'm not really talking about speakers that cannot be driven by just a few watts. The video above, with the Decware amp is interesting, because while this amp probably sounds good within its envelope, at just 2.3 watts/ch, it clearly is extremely limited as to what speakers it will work with. This is basically the other end of the scale, the speakers in my OP need a minimum of 100 watts/ch and an amp that can push current into a very low load. The opposite is the case with a tube amp that puts out flea power...this amp can only be matched with a very small number of speakers. ( Relatively). 

So, while I would agree that the cost to put together a system with a flea watt amp is probably less than one that needs a brute of a ss amp upstream, neither is great IMO. 

I am currently using that same 2.3 wpc amp with my 96dB 140 lb floorstanders.  I feed the amp with a Grimm MU1 streamer and a Lampizator Golden Gate 3 DAC.  Interestingly, my DAC uses large DHT tubes capable of making twice the power of the amp (although they don't, the DAC output is line level with volume control).

Jerry

I like tube amps and generally don't like high powered tube amps so I look for sensitivity in speakers my current AN-J's are 93db and work well on 3.5 2a3 watts. 😉