I have a similar room to yours, and sit a similar distance from the display. I tried to come up with a solution that would avoid the in-ceiling route, but to no avail. What it comes down to is that Triad has designed the In-Ceiling Bronze/8 LCR just for this application. I use them for my front three, and the In-Wall Bronze Surrounds as surrounds mounted in my ceiling as well. I feel that the most important thing in these compromised room layouts is keeping the axis of the front 3 aimed at the listening position, and all firing from the same plane relative to the listener. I don't think it's a good idea to have a mix of in-wall and in-ceiling speakers, as the pans will totally give away their position. Additionally, by placing them in-ceiling, you effectively get the speakers closer to the listening position and don't have as much SPL fall-off over distance.
I went ahead and trusted Paul Scarpelli and took the leap of faith with in-ceiling speakers. I have to say that when you're in the sweet spots (anywhere on the couch facing the TV) you don't realize the sound is coming from a different location than the TV. However, if you are just a little too far forward or off to the side, or tilt an ear towards the ceiling, they become localizable as separate from the display.
If budget is an issue, just get the front 3 first and pull wires for the surrounds. Don't use the cheaper rounds, they are not good for that application, better to save your pennies. In general these speakers are only sold through dealers. They are priced the same purchased from dealers or direct from the company, to protect their dealers essentially. But they are selective about who they let sell their speakers since the performance is very install sensitive. So most dealers have a lot of experience with installs, and many happy customers. Last but not least, budget for 1-2 subs, ideally freestanding rather that In-Wall if feasible for your room, and you don't really need to buy Triad subs. But their LCRs absolutely need to be set to small and mixed with subs to perform well for HT.