Good speakers at low volume?

What you really need is a "loudness" button on your pre-amp. Unfortunately, these are rarely found in "hi-end" pre-amps or integrated amps these days. The reason you need the loudness button: Fletcher-Munson effect and your ears. The human ear is most sensitive to mid-range frequencies. The result is that as the overall volume level decreases, you begin to lose the lower and upper frequencies relative to the midrange. That's why you "lose detail" and bottom end bloom when listening at low volumes.

I'm sure the others here will label me a hi-fi heretic for this suggestion but it really is the only realsitic answer to your situation simply because of the non-liner way the ear responds to sound pressure levels. One can approximate the effect of a loudness circuit using a parametric equalizer. That would be a fall-back solution. You can get good info on this online by Googling "Fletcher Munson Effect".

It seems that most everyone missed the point of my post regarding the Fletcher-Munson effect. The fact is that NO speaker will sound the same at both low volumes and high volumes because of this physiological reason. If a speaker sounds full and detailed at low volumes it will sound bloated and hot at moderate/high volumes. What you are seeking does not exist. Really the only way to make this happen is through equalization (like the infamous "loudness" button I mentioned or through a graphic equalizer/tone controls).