What makes speaker's sound big?

Does a speaker need to have many drivers or a large driver area to sound big and fill the room?
I am asking this question because I have a pair of tekton design double impact and would like to replace them with smaller speakers and a pair of subwoofer's to better integrate the bass into my room.
I just borrowed a set of B&W 702S. The are good but the just don't make that floor to ceiling sound that I like.
Maybe I have already answered my own question (: But again I have not heard all the speakers out there.
My room measure 15x19' and the ceiling goes from 7.5 to 12.8'

You can achieve what you are looking for in a medium sized monitor and subwoofer preferably two.  

The differences within the speaker design (traditional box) that make for a big sound include-

1) Efficiency- higher efficiency = bigger sound / jump factor.  example Spendor A and D series.  
2) Coherence between drivers- perfect coherence and alignment of the drivers so that there are no gaps or suckouts.  The drivers sound as one.  example Spendor, Harbeth, KEF R series.
3) Dispersion.  Being able to disperse all frequencies in all directions has a big impact on sound stage size.  KEF, Harbeth, Spendor.  

Tube preamplification or amplification also helps.  

Subwoofers properly integrated is a must.  
What do you mean by "better integrated" bass? Again I harp on "requirements": Can you give us some more info pls? Do you not have enough? Too much? Perhaps you have a nasty bump in the frequency response someplace and it's boomy? Or bloated? Perhaps it's not a problem of equipment but room placement and tuning. I don't mean to sound rude. I believe that the issue needs to be clearly defined before a "solution" can be offered.
Happy listening.
Mark & Daniels. I have the 1st gen Maximus-Ruby. They use their own version of the AMT driver and a 5" woofer (crossover at 900Hz). Terribly inefficient but with a proper amp they have amazing dynamics and soundstage. The 2nd gen is supposedly even more refined. 
radiating area of drivers
dispersion characteristics of drivers
distance between drivers
baffle design
boundary reflections
When talking about sounding big that usually translates to full extended bass. Powered subs are your friends there. Big = powerful and the bass is where most of the power in music occurs. It takes exponentially more power to deliver flat response as the frequency decreases and that power must be converted to long wavelength sound waves so that pretty much explains it. Tiny drivers/speakers alone are more challenged to deliver full extended bass and all fall short alone to some extent.