Low volume kind to low frequency?

I would consider a biamped monitor/sub type system. This way you can turn up the sub for fullness at low to mid volumes. I used to have my setup this way, with a remote controlled amp feeding the subs. It was great to be able to tailor the bass per recording and for the desired volume. Even if not fully natural, expanding the bottom octaves really increases the sense of acoustic space.

At low levels your brain rolls off treble and low bass. Since not in the tiger hunting human range we dont need wide range at low volumes.

Johnk is correct - the response of the ear is not linear. This physiological phenomenon is known as the Fletcher-Munson effect. The ear is less sensitive to frequency extremes at lower absolute volumes. This is the effect responsible for the "loudness" button on (mostly low end) amplifiers. It's actually a very practical thing and should be incorporated in higher-end equipment to allow for more natural sound at low volumes. One would think that with modern digital technology someone could implement this with little or no signal degradation. Without this compensation, playing full-range music at low volumes will always sound anemic on a system that sounds "right" at higher volumes.

Rick,
I definitely agree with the suggestion of getting a subwoofer with a remote control. It works great for what you want to do.
Regards,
Charlie