The NHT's are one of the few speakers that I have experienced that do well with inside bookcase placement. I used a pair of NHT SB2's in this way for a number of years. With a backless bookcase, the NHT's should do even better. In my friend's set-up mentioned previously, her bookcase is more of an glass and wood, open rack affair. Her room has only window/venetian blinds and light rugs, so the room is pretty minimalist/live. I was very much taken with how good the system sounded. The music played was Talking Heads, Morrissey, and Sinatra.
Besides acoustic suspension design speakers, you can also consider front ported designs. For the money though ($260 a pair at
J&R Music with free shipping), this speaker is very hard to beat.
FWIW, other speakers that I have tried with bookshelf placement and how they fared: B&W 302 (dreadful), EPOS ESL3 (boxy/ nothing special), Wharefedale Diamond 8"s and 9's (good/ much better on stands), Omega Super 3 (if you are not using tubes, don't bother. If you are, then very good), NHT SB2 (very good), Rega Ara (very good).
Regards, Rich