Please suggest bookshelf with best bass response under $4000 pr.


Lately, I've been craving deeper, tighter bass. I'd like to hear some ideas for replacing my Silverline 17.5 monitors. Is this a stupid question, due to inherent limitations of driver size imposed by typical bookshelf dimensions, or might I actually do better with another speaker? Amplification is Wells Audio 150 watt SS Majestic integrated. Source is aging Jolida JD100 tubed cdp (in new year, I plan to replace this with another SS cdp or a transport/standalone dac combo). Thanks ! 
stuartk
Late follow up. . . I bought an Aqua La Voce DAC, coupled with Empirical Audio Synchro-Mesh re-clocker and coax cable, which made me realize there's nothing wrong with my speakers!  The system, as it was configured before, simply wasn't doing justice to the speakers. Now,the bass is amazing. Round,  punchy. It goes without saying that it varies from one CD to another, but, overall, the improvement is huge. The La Voce is available with different boards/chips (see their website) but as it happens, the standard board is particularly adept at bass reproduction. This was  valuable lesson. 
I build all of my own stuff, so I'm not much help on what is out there,  but I can say that I would seek out an MTM.... Double the cone area moving air does make a difference.  Good Luck,  Tim
@stuartk - Congratulations on the new Digital Setup. How awesome for you. You were going to buy a new digital rig anyway and it resolved your quest for new speakers with better bass. I'm glad it worked out for you.......