For extreme dynamic punch from a smaller sized package, Zu speakers should be on your list to audition. For a completely different sound, but, particularly good a lower volume, Audio Note speakers are contenders. I personally find all of the Audio Note line to be extremely musical and listenable and don't have to be played particularly loud.
I don't think you can judge how well speakers will play at lower volume by their size. The most dynamic and full sounding system I heard at low volume had speakers the size of small cars standing on their bumpers (horn-based system). My own system, which is optimized for low volume sound is not so miniature either (2' X 2' x 3.5').