What speakers work with low wattage class A amps

Speakers are very subjective.  That said, one thing I did discover which was quite a revelation, is that a Horn/Dynamic combo design puts me in the Goldilocks Zone.  Phase issues, upper midrange tonality and dynamic contrast all improved.  

My personal experience: I've driven a pair of Dynaudio Heritage Specials and a pair of Sonus Faber Maxima Auditors with a Sugden A21SE with the volume at 9 o'clock with no issues at all; that said, there is also a REM subwoofer in the system. The space is 13x20x10. I'm not interested in head-banging volumes, but I believe there is plenty of room to do so. I've also had comparable results using a PrimaLuna evo 400 and Rogue Cronus Magnum.   I'm going to climb out on a limb and say that wattage, like horsepower, is conditionally relevant. From there I'll leave it to the engineers to thrash out. Best wishes.

Get yourself a pair of full range speakers from Lii Song audio and put them in a baffle board, the Decware/Caintuck speakers are a good model, wide-open, no back or, sides, and no crossover. They don’t do super loud, but there is some kind of magic there.

Tannoy

I'll second @akg_ca

The de Capos are great speakers, I have the earlier de Capo i in red maple