Just to add my two cents, some of it repeating what was said above, I think a sub can help with low level listening, it adds body and little umph to make things pop like they should.
I have also found that treating the room with a mixture of absorption and diffusion can improve listening at all sound levels, but especially at low levels. I thought my Pranafidelity monitors were much better at high levels until I added some ceiling diffusion (in addition to other treatments) and now I listen regularly at 4 - 5 dB lower levels on a routine basis.
Finally, the best low-level speakers I have experience with are the Audio Physic Steps SLEs (not the newer models which are very different) and the Totem Element Fires. Both have full-range drivers (no cross-over) with a supplemental tweeter. The Totems have much better bass and are easier to set-up than the Steps but the Steps, properly set-up, image like no other (at least from what I've heard).
I have also found that treating the room with a mixture of absorption and diffusion can improve listening at all sound levels, but especially at low levels. I thought my Pranafidelity monitors were much better at high levels until I added some ceiling diffusion (in addition to other treatments) and now I listen regularly at 4 - 5 dB lower levels on a routine basis.
Finally, the best low-level speakers I have experience with are the Audio Physic Steps SLEs (not the newer models which are very different) and the Totem Element Fires. Both have full-range drivers (no cross-over) with a supplemental tweeter. The Totems have much better bass and are easier to set-up than the Steps but the Steps, properly set-up, image like no other (at least from what I've heard).