Low level listening

For example class D amplifiers tend to require higher volumes to come alive in the bass regardless of speakers.  

Not really found this to be true.  What specific class D amps was this?

Large horns can be ideal low-level loudspeakers why I use them in my office system.

@johnk 

I'm finding this to be true as well. I recently switched out some bookshelf speakers for big horn tweeters in my system. We're talking 800Hz and up. The narrower dispersion on the horns had a surprising effect of making the room sound more lively and airy than the wider dispersion speakers, and this worked very well towards low level listening. I was amazed at how enjoyable and dynamic the sound continued to be at very low levels. I think it's something to do with direct to reflected ratio being high while maintaining a relatively long reverb tail in the room.

That’s why my Cornwall IV’s sound so very good at low volumes.  

This is a topic close to my heart: I listen to low volume classical ~11-12 hrs/day and so it's important to me that I actually hear the music. From long trial and error, I found 2 interrelated factors that help with this:

1 - Use relatively inefficient/insensitive speakers. The two pairs I switch between now are both ~83-84 dB at 1M. It takes some juice to drive them, which means more play on the low end of the volume pot of whatever preamp I use; and

2 - Use sealed/acoustic suspension speakers. Both pairs I have are sealed. Somehow this lets more clarity flow from the speaker at low volume. There's no port to hear or deal with.