Best Late Night Low Volume Speaker

Quad electrosatic, they stay natural and realistic at at low volumes.

I always liked my Spica TC-50's with my Music Fidelity A-1 (the original) playing the classical radio station out of NYC on low volume, used to just leave it on all night..

I agree with Beavis, I've gone from Vandersteens to Magnepan 3.6r's and both needed at least 85+db spl to sound dynamic with my Classe 400 watt amp.

After listening to speakers with no crossovers with high efficiency along with tube amplification there is no going back.My ears thank me for it.

Check out the Zu Audio speakers as they might do well with the gear you already have.

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.