Recommendations for speakers that sound great at lower volume levels.

I’ll give another endorsement for British mini monitors. I have small to smallish listening rooms. I also listen more times than not,at low volume. My Graham Chartwell LS3/5’s do a wonderful job at low volume. They soundstage freakishly well. I also run them with a couple low power First Watt amps. They will always be in the rotation for me. The great thing with these mini monitors,is you can flip them if you don’t like them,and probably break even at worst. 

I think the persona B could be on the list. 

+1 on the LS3/5a... had an 11ohm set of Rogers from the mid 80s and just loved them. Wish I still had them... playing a set of Equation "7" these days that are just incredible in my kit. Listen late night in a dead quiet room and paired with a Cary tube amp and Manley Shrimp tube pre they are incredible. Won't find much on the web and the distributor in Canada, Mutine, got beat up pretty good on here a while back but they are special. All hand made in Belgium with the finest components and internal wiring. Had no idea what to expect other then they mated well with
low powered tube gear. The "7" were the bottom end of their line and retailed for $3K in '05. Said to be perfect symetry between Equation speakers and Audiomat electronics; the Arpege integrated specifically. Have heard the Audiomat gears and sadly never got the chance to pair them togther. Anyway, fabulous at low volume - everything's there full and robust. A real treat if you can come across a set. Maybe $13-$1500 depending on condition; worth every penny. 

I owned the Harbeth SHL5 Plus and earlier versions of the SHL5 and they all sounded great at low volumes. I actually bought them for that reason. The issue is more likely to be your amplifier. Harbeth's, when used with SS amps like Ayre, Aesthetix, Naim, Musical Fidelity and many others excel at low volume. 

I've have never heard a Harbeth speaker that sounds good with any tube amplifier though many others will disagree. If you like your amp you should work with a Line Magnetic dealer to find the right speaker for your requirements. You might also find a dealer who would loan you a SS amplifier to try in your system to see if the Harbeth's might actually meet your low volume needs.

Good Luck!

I have Salk Exotica Raal monitors.  I can highly recommend them for low level listening.  I marvel at the sound every day.  I listen a good portion of the day while working.