What makes a speaker sound great at low volume?

     Interestingly, I noticed an unexpected improved low volume listening performance when I switched amp type from an Aragon class AB to a class D amp of about the same wattage.  The improvement was significant even though I was using an older pair of Magnepan 2.7QR large panel spkrs that are fairly inefficient (87db @ 1 W).  
     I'm familiar with 'loudness' controls and would equate the improvement to their affect; a perceived increase in the bass and treble to compensate for the proven reduction in perceived bass and treble when listening at low volumes.  
     What I found especially noticeable and beneficial with the class D amp performance was that the proper bass and treble presence maintained its proportional accuracy at all volume levels, from soft to very loud as if there was a 'loudness control' continuously engaged. 
      I cannot verify that all class D amps share this ability, however, I currently own 3 different brands of class D amps (ClassD Audio, Emerald Physics and D-Sonic) and they all share this ability or characteristic. 
     I would also agree with the several other responses on this thread that  stated moderately high efficiency speakers would be beneficial for improved low volume listening performance.

Tim
 

No crossover. Tube amp directly driving the woofer...

+1 .. my Decware/Omega pairing continually surprises me with the level of detail and dynamics when listening at low volumes levels. 

A few people have suggested ESLs, and I'm pretty sure they'd fit the bill. I had ESL's with a McIntosh set-up, about 40 years ago, and they were very good at low volumes. Mind you, the MX-113 tube pre had bass and treble controls, so that helped. They also had a dynamic low-frequency driver ...

High eff with low power its not hard to find low noise amplifiers.

Many thanks for a lot of inspiring input. I have enjoyed reading the responses including the recommendations for other ways to improve SQ than replacing speakers.

My selected take-away for now is
- go for high sensitive speaker (above 92 DB)
            - eventually go for Horns
            - eventually go for studio monitors (or mid size speakers) 
- add EQ in some way, either via DAC, Pre-AMP or room correction
- replace current AMP with a Tube-based AMP

I will start with the speakers and move down the list - and replace my DAC at some point. 

Many thanks. Michael