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'

martin-andersen
Martin, no point source speaker is going to produce a life sized image. What you get out of them is a mini sound stage like you are sitting all the way in the back of the hall. Another problem is the sound pressure level of point source speaker drops of at the cube of the distance, very quickly. Linear Arrays or Line Source speakers produce a large image like sitting up front. Sound pressure levels drop of at the square of the distance, much slower so Line source speaker project sound better. In order to perform as line source a speaker has to be tall, preferably from floor to ceiling which unfortunately does not suit many people. Also unfortunately, everything else is just wishful thinking. You can be sitting in front of the biggest Wilson but close your eyes and you get the sound stage of any run of the mill floor stander. This is one of the reasons people love their Magnepans. Except in the bass Magnepans give a more life like sound stage because they function as line sources above 150 Hz.
I'll mention another element. Right amp makes speakers sound good and big ! Give speakers 'the current' !
I don't listen to orchestral works often, but my little KEF Reference 1 monitors create a bigger soundstage and image better than any of the much larger speakers I've owned. Combining them with four subwoofers doesn't hurt either. 
MC give it a break, you never even heard the op’s speakers. The OP wants to get a different speaker and yes, they will be much better than what he currently has, it won’t take much. You don’t need large drivers to get big sound. Some of the best sounding speakers use multiple smaller woofers to get full sound. For example, look at raidho, revel salon 2’s/studio 2’s, and others. 
There’s not really any substitute for BIG drivers and LOTS of them! The most “you are there” sounding speakers I’ve ever heard were a pair of Ezekiels; twin 15” woofers, twin 10” mids, a three inch Mylar dome tweeter and one ultra-HF horn tweeter in each cabinet. With good audiophile grade vinyl, or reel-to-reel tapes; you literally couldn’t tell the difference from a live performance. We used to go hear Steeleye Span and the Seldom Scene at local DC clubs all the time.  The sound was IDENTICAL!
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.

db 
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 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! 
There a a million factors that dictate how big a speaker will sound.  The key factor is output coming out of the speaker, not in terms of SPL or sensitivity but dampening.  A box that is well damped will have minimal cancelation inside.  

Tweeter dispersion is incredibly important.  Ribbons and AMTs that spread around sound will sound bigger than a single dome tweeter.  

Do they rely on room reflections to build the soundstage or do they sound better when the room is heavily damped?  How is your room designed.  A speaker like MBL Radiastrahler 126s will sound massive in a room that is energetic but will disappear and sound small in a room that is over damped.  

The crossover design impacts this.  I find that the steeper the curve the less energetic a speaker is and the more you need big drivers, arrays and/or tons of power.  

There are a million different ways to accomplish this.  Open baffles, electrostats, composite cabinets, integration of room treatments, etc...

It really depends on what you want, aesthetics you can live with or find exciting/interesting and what your budget is. 

An extreme example is the Wilson-Benesch Endeavour.  It is a stand-mount speaker (that is $50K) but is an incredibly well made cabinet and has a monstrous output in terms of imaging and soundstage. 

Another example is Audiovectors R series with rear firing tweeters and/or midrange drivers depending on the model.  These sound much bigger than they are.  

In the end, they may not be complete substitutes for a large floorstander but you can get close enough to be happy.