That's a great room for those speakers! My junk is in a very large room, bigger than that, but space off the front wall is an issue for how things need to be for walkway past that spot. We have a few unused bedrooms in the back of the house that share a wall. I have thought of knocking the shared wall down which would create a 11'W x 24'L x 9'H room. The only thing I don't like about the idea is I wish the width were a bit more... ~13'W. I'm also considering knocking down an exterior wall for one of those bedrooms and adding on square feet to get the width larger.
What I don't know, and really wish I could "test drive", is whether going thru that trouble and expense to get more width is worth it. I wish I could test drive the 11'W x 24'L x 9'H setup. That could be "Good, Fast, and Cheap"... the (other) Holy Trinity.

If others have experience with that sort of space, I'd like to hear about it.
It's good to hear the subs can handle that larger space. I've been hesitating on "double or triple", but leaning toward Double. I think I'll pull the trigger on doubles now, but modular... so they can bookend my 2-way speakers... which I'll always have an affinity for.