I would consider a diagonal set up for a room of that size. It will really help the imaging and you'll be able to place the speakers closer to the walls, so you'll have more "room to live".
I have a 12x14 room and the biggest improvement I've ever made to my system was setting up on the diagonal.
Check out www.decware.com and look under Articles on how to set up a dedicated room on the diagonal. I think the article is called "HOW TO SET UP A DEDICATED LISTENING ROOM WITHOUT FANCY TREATMENTS" or something.
OK all the furnitue is out of the room and I set the system up on the diagonal....
Holy Cow!!
I cannot believe how dead the room is without ANY furniture or ANYTHING on the walls. On a simple Onkyo Receivere and Speaker system the image reaches about two feet behind the speaker placement. That is just beyond what this system should be able to do! I can't imagine a setup where I'll be able to do this at home but what a great find!
+T for the lookout!