I would go with three subs using the principles made popular by Dr. Geddes.
Two in the front of the room and one in the rear of the room, near the ceiling (upside down sonotube can accomplish this).
http://www.avsforum.com/avs-vb/showthread.php?t=1124011
Two in the front of the room and one in the rear of the room, near the ceiling (upside down sonotube can accomplish this).
http://www.avsforum.com/avs-vb/showthread.php?t=1124011