What makes a speaker sound great at low volume?

chayro: Love your first sentence ...

OP: I don't know if you're considering vintage speakers as well, to solve your low-level, listening issue, but I have a pair of Kef R107's, and they produce a wonderful sound-stage no matter where you are in the room. They are supplied with a small EQ adjuster that is electronically, part of the crossover. At low volumes I just boost the Contour adjustment dial. (This is the only time I touch the contour dial). This seems to add what's required to cover all the necessary frequencies, and the music sounds great.
Most people seem to like the 107s, but some just don't. They're a little different.
Anyway, just my two cents ...

A few people have suggested ESLs, and I'm pretty sure they'd fit the bill. I had ESL's with a McIntosh set-up, about 40 years ago, and they were very good at low volumes. Mind you, the MX-113 tube pre had bass and treble controls, so that helped. They also had a dynamic low-frequency driver ...