well I listen to primarily music and dual xv15's work much better than a single. my room is 2400^3 that has a 6'x7' opening to the rest of the house. However like i previously said, I like alot of bass and headroom. until he provides more information on his goals and listening habits we are both shooting in the dark.
Typically House music for me and country for the girlfriend.
I like plenty of bass but I'm limited on placement if I were to go with a dual setup. One sub in each front corner of the room on the same wall as the TV. Rest of room is all open living room / kitchen combo.
It's a 14x32 rectangle with 9ft ceilings. Seating for TV viewing is around 10ft from the TV wall, but most listening is done while walking around the main level of the home.