Recommendations for speakers that sound great at lower volume levels.

For times when you need to listen at low levels, why not get headphones?

+1 on the headphones or just use the loudness control. That’s what it’s for. 

A great low volume speaker is a pair of stand mount Fritz Carerra BE Speakers. I recently picked up a pair and they are fantastic.

i agree 100%, low medium high volumes... fritz’s are superb standmounts

Every single loudspeaker you will ever own will do the same thing. Actually, it is not the loudspeaker. It is your ears. Better yet , it is everyone’s ears. Google Fletchur-Munson curves.

not so simple, nor absolute

while fletcher munson always applies in a technical sense, in the real world, some speakers are at their best when playing at somewhat louder volumes, based on their design... for example, buchardt s400’s have a rear mounted passive radiator that really works well at medium to higher volumes, the bass then becomes full, powerful, room filling, all around terrific... at lower volumes, not so much...

...in contrast, a terrific smaller monitor like a ls3/5a has very limited absolute volume capability, and is best listened nearfield, semi nearfield, and at lower to medium volumes

Matching amp with speaker is, perhaps, the most difficult and central issue in Audio.
It is clear that the 26 watts from the LM is not enough power for the Harbeths. However, I imagine you love that amp.
+1 on Quad 57s. That amp is a beautiful match for Quads!
And the SQ of 57s is still about the best midrange you can get.
And the rebuilt ESS Quads are said to do bass and treble unlike any 57. Harbeths are lovely but cannot compare with the beauty and enjoy ability of 57s. After 64 years, still one of the best.

I have a pair of Tekton 2-10 Perfect Sets which I drive with a pair of Schiit Aegirs - 80 watts each heavily biased to Class A.

They are amazingly good at low volumes.

About $2k/pair for the Tektons.  Great dynamics, detail and when you sit down to listen, it’s very hard to leave - even at low volumes.

If you’re not bothered by big heavy speakers, get the Tekton Moabs-even better.