I'm still debating the single M80 vs. dual VP180 center channel arrangement. Right now I have a single M22, and it hasn't really disappointed me at all, but I still like the idea of a) having matching M80s across the front, just because it's supposed to be ideal to have them all match exactly, or b) having horizontal centers both above and below the screen to anchor the sound to the screen. I could have an M80 directly behind the screen if I went with an acoustically-transparent screen, but I don't think I want the extra expense and the slightly compromised sound and picture. I have some time to make up my mind. I'll be interested in what you decide works best for you, too.
