Best Late Night Low Volume Speaker

AKG K1000 "earspeakers".
If you want real speakers, I would try very high sensitivity speakers (preferably horns).

Harbeth SHL5 that I owned were fine but the Living Voice OBX-RW that I own now are much more resolved and balanced at low level listening.

I FACE my panels at one another and sit between 'em.
It's like wearing 'ear speakers', but without anything clamped to my head.
Maggie Magic is alive and well even at 0-dark thirty is a quiet house.

Quads. IME, I disagree with the Harbeth recommendations.

I use my Merrill single drivers all day long as computer speakers. Great with low level listening. The other advantage of small single driver speakers is there really is a lack of bass to disturb others at night.