Mike,
Per Dolby Labs and my recommendations, the main QS8 surrounds are best to each side of the listening area, and a bit to the rear (up to 10 or 15 degrees from an imaginary line drawn across the listening area from one side wall to the other) and "well above ear level" if possible--about 2 to 5 feet. Put the rear surrounds at roughly the same height as the side ones, and do not aim them at your head. Separate them by 4 feet or more.
The center can be below or above the screen and aimed up or tilted down towards the listening area. If the screen is really large, you may find an odd dislocation of the dialog from the actors on screen, in which case you may want to try running two centers in parallel, one above and one below. That way, the phantom image will appear in the center of the screen, exactly where you want it. Depending on your installation, one center may be excellent, but again try above or below-screen locations before you drill holes. Listen for the most neutral tonal balance that matches your front mains. The center will never sound identical to the mains, but close enough that dialog or sounds do not sound disembodied or distractingly colored.
Regards,
