Creating a Large Sound Stage

I think that sound coming from outside the speakers is mostly a product of the recording unless you have some specialty speakers with drivers or waveguides designed to throw sound to the sides. I spent several years working in recording studios and we had devices that could widen the soundstage by manipulating phase, but I didn’t use them. If you reverse the phase on one of your speakers, the image will spread out past the speakers, but you lose the center image and bass. Try it if you want to see how phase affects the sound. 

Recording, room acoustics, speakers, electronics, cables. In this order, provided you have decent electronics and speakers. 

Don't forget that speaker placement also has a lot to do with good sound stage.