The thing is, stereo sound is recorded that way. Left and right. Movie sound is mixed, not that way, with dialogue placed in the center channel. Some have used "phantom center" with success, but I wouldn't do it personally. As I looked over your post, it occurred to me that you possibly meant using the "stereo" pair wired from the center channel to provide a phantom center, and use "wides" as the L/R. That would be totally unsuccessful and I hope my alternative interpretation is wrong. So no, stereo sound behind the screen would not be more realistic.