My suggestion is warm-voiced full-range electrostats. In my experience good electrostats have superb clarity at low volumes, so you can hear everything that's going on. I often listen at 50-60 dB, and I can hear everything that's going on. You want a warm voiced speaker (like the Sound Labs or Original Quads) because the ear has a harder time hearing low frequencies at low volumes. The dipole bass of a full-range electrostat will minimize the amount of bass propagated through walls to bother people; you'll be putting 5 dB less bass out into the environment than with conventional speakers. With tall line-source approximating electrostats like the Sound Labs I sell, the volume falls off more slowly with distance, which would be a slight drawback late at night. The generally point-source approximating Original Quads wouldn't have this problem. The 63's are also a possibility, but the Originals sound sweeter.
So my suggestion for the ultimate late night nirvana speaker would be a pair of Original Quads. To warm them up a bit, shorten the legs so they sit closer to the floor or give them a solid stand to eliminate cancellation between the bottom of the speaker and the floor. And if you want the ultimate in clarity, have Ben Openshaw, aka The Electrostatic Doctor, replace the stock diaphragms with lighter, thinner diaphragms and perhaps even give you dual power supplies, one for the bass panels and one for the treble panel. The only potential disadvantage of the Original Quads in this application is their narrow sweet spot, but for the kind of listening it sounds like you're contemplating that might not be an issue.
Best of luck in your quest!
So my suggestion for the ultimate late night nirvana speaker would be a pair of Original Quads. To warm them up a bit, shorten the legs so they sit closer to the floor or give them a solid stand to eliminate cancellation between the bottom of the speaker and the floor. And if you want the ultimate in clarity, have Ben Openshaw, aka The Electrostatic Doctor, replace the stock diaphragms with lighter, thinner diaphragms and perhaps even give you dual power supplies, one for the bass panels and one for the treble panel. The only potential disadvantage of the Original Quads in this application is their narrow sweet spot, but for the kind of listening it sounds like you're contemplating that might not be an issue.
Best of luck in your quest!