Does Wilson Sophia Sound good at low volumes?

I can't comment on the Wilsons but my N802's sound just fine at low volume levels (70db range). I would get rid of the solid state amps and switch to a good tubed amp. The upper bass and lower mids will become fuller allowing for a better balance at lower volume levels.

If I recall correctly you need to consider the Munson Fletcher effect hearing effect. At low volume levels bass is attenuated relative to the rest of the range. So a speaker with ideal laboratory response won't sound as good at low volume levels as it would at higher levels. Audience-please correct me if I'm wrong.

Anything Spica will sound good at low volumes, but will not get loud. Audio Physic Virgo II and Step (late 90s models)will sound good at low and high volumes, as will Sonics by Joachim Gerhard Allegras.

As I recall, the Fletcher-Munson curve mapped the sensitivity of the human ear, frequency on the horizontal axis and volume on the vertical. As volume decreases, the ear is less sensitive to the low and high end of frequency plot as volume decreases. The "loudness" circuit on some receivers is designed to compensate for this decreased sensitivity at low volumes, increasing the low bass and high treble. For a time, Yamaha even made some receivers with a "loudness" control that was a rotary knob. The idea was you would turn the volume up as loud as you were likely to listen, and then decrease the volume of sound by turning down the "loudness" control...which changed the equalization to increase the low bass and high treble roughly along the Fletcher-Munson lines as the control was turned.

The performance of a loudspeaker at low volumes has very little to do with the associated amplification, except for the amplifier distortion and noise levels. The Fletcher-Munson loudness curves are far more important. The speaker drivers may or may not produce much sound at low volume, depending on efficiency, moving mass, surround stiffness, etc. For example, an acoustic suspension mounted conventional cone woofer with a rubber surround may be very sluggish at low volume. These factors help explain why compression drivers, field coils, electrostats, plasma drivers, etc. perform more linearly at different volume levels and give much more detail at low levels.