Were it me, I would do everything I could to have the front 3 channels forward-firing near your screen.
Possible solutions:
Use L, Center, R In-Wall rather than ceiling-mount speakers. With many manufacturers, the same speakers are used as ceiling-mount, but different baffles (usually paintable, often rectangular vs round).
If for some reason you can't mount in the existing wall cavity, have the builder build out a second wall to mount the speakers, which could also serve as the mount for the display, if desired. It does not have to be deep; less than 12", say 6~8", is certainly doable, and not much wider than necessary to fit the display and L,R speakers. Or whatever width you feel looks best.
There are many ways to achieve the above in an aesthetically pleasing manner. Part-wall (ceiling to top of display), floor to ceiling, etc. Have your builder, installer, or designer sketch out a few options and go over with your wife. With in-wall, you could even have the display and in-wall speakers hidden by curtains or drapes that open when you want to watch movies or TV.
This could be a nice feature, done right, that the wife might love.
You could, at the same time, consider an in-wall type of subwoofer as well.
Use L, Center, R On-Wall speakers (eg Axiom, Anthony Gallo). This would be an option you would consider if you want the HT setup to be a feature of the home, always on display. The Gallo's in particular are very compact and with the accessory wall mount, can go almost anywhere. They are true HiFi speakers, although I would consider using a different subwoofer than the one they sell.
http://www.roundsound.com/satellite-speakers.html
Your side/rears can be in-ceiling with either setup, which could be 5.1, 7.1, etc.
