Even in my twenties I didn't like to have a stereo be so loud you couldn't hear someone else speak. All those decades later, I can't handle loud volume, period.
Re this: "To me, one of the most important subjective measure of a system is how it sounds at low volume."
@larryi, how right you are! I've listened to low volume music while working in home office for 25+ years. I've had a number of systems over that time. I found that sealed/acoustic suspension designs + a subwoofer play better at low volume than ported designs. Never heard horns, ribbons, or other high efficiency designs, so can't comment on those.
At least in my home office, I get terrific low volume sound from either the ATC SCM 12 Pros or the vintage KEF 103.2s. And with either pair of speakers, on those occasions when I feel like cranking it, the walls shake.