What makes speaker's sound big?

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. 

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. 

I'll mention another element. Right amp makes speakers sound good and big ! Give speakers 'the current' !

Give it a rest

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.