Low level listening

A good speaker should play well at very low and very high levels - so I would agree wth Duke. Although this kind of speaker is very expensive and is typically used in studio control rooms where it is crtical that the tonal balance remains unaffected by variations in listening levels.

If you only listen at low levels then you can probably find a much lower cost speaker that only plays well at low volumes...in fact you may deliberately choose a small speaker with less dynamic range over a large speaker as some audio compression may actually improve the audibility at low levels ( where you may run into ambient noise floor problems from AC's etc.)

I would not worry too much about sensitivity given your low volume level requirements ...just audition and select a speaker you like. There is no rule of thumb that says high sensitivity is better than low sensitivity. In fact, I would stay away from extremes in sensitivity as speaker design is all about balanced compromises and an extreme in one area often implies a bigger compromise somewhere else.

Plato,

Good points....perhaps you explained it much better than I did....some audio compression and colouration at low listening levels can actually sound better compared to a perfectly flat speaker (unless you know what to expect at low levels). Mix engineers know this....when they mix something intended to be played very loud then they tend to mix the bass to sound a little thin at lower levels just so it will sound full and accurate when cranked up.