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'

I have a pair of Ohm Walsh Sound Cylinders. They have an 8" driver crossed over at a high frequency to an upward-firing dome tweeter. They are capable of room-filling sound and 3-D imaging - from any listening spot! Bass quality is deep and full, so no need for sub's! Truly a remarkable design! 
Um, you have terrific speakers, and are looking for something worse. Is that right? And you expect to be able to get worse, yet somehow magically have it sound better. Alas, I only work in reality. Add a couple more subs, forget big you will be enveloped. I only go forward, never back. Sorry. But if you really are determined to screw up a good thing you don't need my help, plenty of others here happy to help you out.
I had the same experience as OP's with my KEF Reference 1s, they sounded great for jazz and baroque, but less satisfying for large orchestrations than the KEF Reference 107/2s they replaced.  So I carefully went through the setup of the Velodyne SMS-1 bass manager and the  pair of HGS-15 it manages, changing all the cables AND resetting the crossover from 40 to 80 Hz.  Magic happened.  The setup is as satisfying as ever for jazz and baroque, but now also has the spacious soundstage for large orchestrations.  A Mahler symphony sounds grand again.

Deep bass
wide dispersion 
dynamic transients