I'm going to have the same problem with my 7 foot ceiling on my downstairs ht project. I haven't given up on it, just need more time and money. My original intention was to mount in-cabinet M80's upside down behind an AT screen (Or M60's). I've even given some thought lately about mounting 3 VP160's vertically behind this screen. It'd take up much less screen space. I know there are arguments about sound dispersion with centers, but if the horrizontal dispersion problem is ultimately fixed with the VP160, I don't see why they wouldn't work as execellent behind the screen speakers?
