Ok. Here is what my entertainment center looks like face on. The center seat is 12 feet from the TV (55" Panasonic plasma).
View attachment 21448
The bookshelves where speakers could go would be directly below the TV in the 6" tall section. That's about 51" wide or so. The mains could go inside the bookshelf just above where I have the Receiver shown (even though I don't have one there). That's where I would want to place it. Reason: the other good place for it would be the 6" tall section with the TV box. The problem is, it is ONLY 6" tall and only slimline receivers will work. BUT, the problem with this is, the speakers would be higher than optimal and the very bottom of the bookshelf speakers would be about 44" off the ground (my ear height). In this case, the tweets would be kinda high. Soooo, another place for the mains would be hanging on the OUTSIDE of the entertainment center. You see where I have that little dot with the 44" dimension? That's about there I'd place a bookshelf speaker. In this case, I could get the tweeter right on target. The 30 degree left and right points are VERY close to where that dot is drawn.
The lower right section where you see "sub", that's where my current sub is for my Bose 2.1 CineMate II. That should work.
The room is 26 feet wide (right to left as you look at the image) and 22 feet deep (direction of the speakers). BUT, that 22 foot dimension opens up the the kitchen and dining area and that adds another almost 30 feet. The ceiling is almost 18" high.
With all this now, I guess the question for you is, where would you put the mains? Is having a extra long center channel advantageous here or is something simple like a DT ProCenter1000 all that's needed?