I can't say I agree with all of Doug's opinions in his posts here. Lots of good stuff, but some stuff that I don't agree with. One in particular is large room verses small room regarding ease of design. One is no easier than the other. Both have their issues, and once addressed, will result in terrific performance. It comes down to scale; the quality of the sound over x number of seats. The smaller the room, the tougher it is to deliver a uniform experience, especially with regards to low frequency acoustic response. It's a matter of math. The math helps a larger room in the LF range.
Tnedator, listen to Dennis. This is a room of very good size and proportions. You can get a good-sized screen in there, and at least two rows with very good low frequency acoustic response.
Dennis is totally right to suggest horn designs in this room ... for one reason. As rooms get larger, they have more influence. To know which type of speaker to use, you must be able to anticipate or design for "critical distance." If your LCRs to primary/reference seat distance reaches or exceeds critical distance, you will have an imprecise front stage at that seat. Since home-sized theaters can be so easily over-absorbed with treatments, it becomes advantageous to choose speakers with higher directivity index (some call it controlled directivity) in rooms this size and larger. Horn designs (and good waveguides) have higher directivity therefore it is easy to keep the listener inside "critical distance." The challenge can be covering the primary seats smoothly with speakers with high directivity (especially smaller rooms with shorter throws). Those LCRs must be aimed (including KL-650-THX).
The theater in the attached photos is almost exactly the size of yours. I designed the basics, but used Dennis as a consultant, and to generate the plans. I chose the speakers and designed the acoustic treatments with another colleague to have broadband absorption but retain acoustic life and have a low noise floor. Klipsch KL-650-THX LCRs, KS-7800 THX surrounds (two on each side wall, and two on the back wall), and the two subs from that line. All were concealed behind fabric.
I've used that Klipsch line a lot and still have them at home (a much larger family room). They sound great for all types of sound. I'm sure the big 212s and such will out scream them, but that's not my benchmark in any room.
The Procellas would also be awesome, but pricey.
If it's a big room, these are okay. They have the ISO roll-off ("SMPTE/ISO2969 Curve X high frequency de-emphasis")... which is inappropriate for a smaller acoustic environment. That is not a problem in a large volume and/or acoustically lively room.