SPEAKERS, SPEAKERS AND MORE SPEAKERS.. BUT NEED BASS.?

How much money you got? 

Hi Shinemaster,
For your budget I would look for used. The vintage Sonus Fabers tend to be a better build than the new models. Vandersteens are solid.

You may want to check out these guys as well, specifically designed for small environments. 

http://www.devorefidelity.com/

I hope this helps as I believe it touches on what your considering and what people have suggested in some regard. 

I have a pair Sonus Faber Cremona. The original Serblin design with the scanspeak drivers. A few years after I purchased them I decided I needed a bigger sound stage and more bass. Everything I was looking at was astronomical in price. More than I was willing to spend.

What I realized was that the bass drivers from most of the speakers I was researching were/are active drivers.  So I began to check out Subs to add to the Cremonas. The idea being that they would become the active drivers. 

I ended up with a used pair of REL B2  I have them connected through a Neutrik cable which integrates extremely well with the system. Not only did the addition of the subs bring out the desired bass, It enhanced the entire sound stage. Imaging, Clarity, Texture, Depth. It was like I purchased a whole new system.

Inspired by the addition of the Subs I added the ELAC - 4Pi plus.2 Super Tweeter to the system to expand the upper frequency range. I have pure silver cables that connect directly to the speaker taps for a seamless integration. Now the system is beyond anything I ever imagined it would or could ever sound like. 

Summary
2 Used REL B2  $ 2,200
2 Used Synergistic REL Neutrik Cables $1,500
2 ELAC 4Pi Super Tweeters $2,700
2 Pairs 1M Tempo Electric Pure Silver Speaker Cables $465

Total upgrade cost $6,865
Original Sonus Faber Price $8000.
Total Speaker Set Up Price $14,865
Frequency response on paper 13hz - 55khz
Most probable frequency response with room constraints 22hz - 50khz

Pros :
It sounds as good and in some cases better than speakers that list for
6X more.( I have done comparisons)

My kids can still go to college.

Cons:
Bulky, Not Sexy by any stretch of the imagination.

Took a long time to piece together.

Best of Luck on your Journey

you might want to rethink the use of a sub with Vandersteen new SUB 3 with same capability of the Quatros sub and can be tailored to any room 

Or possibly don't waste money buying modern stuff that will loose half its value the moment you walk out of the store with them :(.
Be patient and wait until a mint pair of TDL Reference Monitors become available. I promise you will not be disappointed. You won't be able to listen to them if you have loose bowels though. I'd forget sub-woofers, instruments of the devil.

 @audiokinesis  "The net benefits of not using a highpass filter were greater".  Hello, Duke.  You bring up an excellent and mostly overlooked point regarding subs and crossovers.

When I purchased my Coincident speakers, which consist of satellites and subwoofers, I could connect the subs to the sats using the subs' crossover, or not.  My experience mirrors yours exactly