I think the basic tonal quality of the speaker has a lot to o with how it might sound at a lower volume. For me, highly accurate, analytical, or 'resolving' speakers lose even more body as they are turned down. +1 Sonus Faber, Rockport, Joseph, et al.
An amp can have a lot to do with low level body and resolution. I moved from a W4S STI-1000 huge Cl D integrated to an Odyssey Audio Kismet stereo amp a month ago and the microdynamics and detail I now hear are even more than I thought possible at 65-70 dB listening when reading. It draws me in.
Finding speakers amp that sound nice at 60-70db with no equalization in the audio chain will mean that same set up will probably be unusable at real volumes. You'll have to pick if EQ is a no-no.
So, love or hate DSP, I will say that the DSPeaker Anti-Mode 2.0 I use for room correction, and some minimal eq lowering, has made the sound of my two-channel system very audibly better. I don't think folks understand how low, flat bass (non-room-lumpy bass) can sound so stunning when controlled.
PLUS the unit has the equivalent of a loudness control for both bass and treble curves easily used on the fly. The speakers in our room, Raidho D2s sound clear as bell, and luscious at 65dB with bass that'll stun you despite how quiet it seems.
I vote at the very least for a loudness control, and at the very best, one of the high-end DEQX units that I've lusted after. It could be tricky otherwise unless you're willing to give up the best sound at one end of the volume chart (low or not low). Good luck. Keep asking and researching.