I've had to contend with sloping ceilings in both my systems (work and home). I'm currently struggling with the same question at home and am inclined to offer up my experience so far, to see if it may help, and to see if I can get any advice of my own. In my case I'm locked in to a configuration already so my questions are limited to treating the room.
My work system works out wonderfully: it is a rather large space, approximately 20X30 feet, with sloping walls on both long sides. The system and speakers are against the the lower part of one of the long walls with the slope rising up above them (as if they would be in an amphitheatre). Soundstaging is wide and deep and it all works out splendidly there.
The home system is just the reverse: the listener is seated under the sloping wall on the low side. This room is closer in size to yours, being about 10' X 25'. The slope in my room goes from about 8 feet up to 11.5 feet. This configuration does not work as well with the bass being a bit boomy, and the soundstage seems compromised and lacking focus. I'm speculating that the ceiling is going to require some kind of treatment to kill that reflection. If I had the choice, because of my experience at work, I would start with trying the speakers at the low end of the slope rather than the high end. A TV screen in between is definitley a compromise to imaging in my experience too, but when listening to music I've found that just throwing a blanket over the screen helps..at least acoustically (certainly not a visual highlight though).
Good luck, and keep the posts coming as you try to figure it out.
Marco
