I recently re-arranged my room where my Home Theater system is set-up. I have an AR 15" sub, which now is on one side of the listen area and because of that, I have imaging problems. Unfortunately, due to its size, that is the only place it can be placed. To remedy the situation, I plan to replace it with two smaller subs on each side of the TV. Which would be the better route to go two 8", two 10", or two 12" subs ?. Another 15" would be absolutely overkill. The room is approximately 16' x 20' with a vaulted ceiling.