Just a thought... I wonder if electrostatics might work well (e.g. Quads) as they have nearly no side wall issues and you could put them close to the walls. Since you have plenty of length, you could move them well out into the room. If modes are an issue, is one of the end walls blank? The idea of building a closet, or even built-in storage cabinets on one end of the room is not bad. With my Quads, I've built diffusors on the front wall, to tame the back wave from the quads without losing its energy. What are other's thoughts on this idea?