In my modest size room (2150 CF) the VP150 has no problem.
You can adjust the center level as needed to ensure equal output across the fronts and center.
I think most people who advise using 2 vp150's do so because they have large screens, and having one above or below the screen can cause the dialogue to be 'disconnected' from the screen. Having two vp150's (one on top and bottom) can center the dialogue directly in the middle of the screen.
I have not noticed anything with my 150 that would indicate I need two (although it probably wouldnt hurt)
Sir quack may have better advice since he has an 8000+ cf room
