On another note; by all means, do get some subs into the room. With a large space, the mains alone will not do the job.
I have a 10,000 cubic foot area, open on one back side as you have and with an 18 foot vaulted ceiling. I run a pair of monster Bryston Model T's with the external PX-1 super duty external crossovers (to prevent melt downs). The amps are Anthem M1 mono blocks at 2000 watts per channel. As great at the Model T's are and they are great, a little help from subs really moved things to a whole new level.
I am running Three subs in the room; more is better. An EP-800v4 with "the switch", EP-500 and a Bryston Model T Sub with a v4 modified amp and of course the "the switch". One sub at each flank of the room and the EP-500 at the rear.
Allow your subs to do the heavy lifting for the low end and let the mains do what they do best.
