I would not make any choice based on theoretical advantages or disadvantages of particular designs. Big bass drivers in horn systems are out? Some of the best low volume systems ARE horn systems with gigantic woofers. I’ve heard dozens of systems with 18” woofers; my own terrific low-level system has twin 12” drivers. You can find good low-level systems from a wide variety of designs. The Volti horns, Charney fullrange single driver systems, Devore and Audio Note two-way box speakers are good examples people here have suggested. The two-way system with multiple tweeter arrays of Tekton are also good at low volume.
At extremely low volume you are not going to get deep and impactful bass. What you need is something with clean bass down to 50-60 hz and a very good and lively midrange. This is where most music resides and so upper bass to upper midrange matters the most. I tend to like horn systems that do well in this range, but, as noted above, other kinds of systems can do the trick too. My own personal choice for low volume listening would be a good horn systems, Charney Audio Companion fullrange driver system, or Quad 57 electrostatic speakers. If I were listening only at low volume, I would go with the Quad 57.

