Well as noted, multiple subs are most effective for smoothing bass response throughout the room, while also adding headroom and reducing distortion. My thoughts are usually to buy the single best sub you can afford now, and then start saving right away for a second one. If the pb1000 was ok, then you will be very satisfied with the 12s. Then just get another as soon as you can. If it were my room, I would work on the front wall and speaker/tv placement. I would recommend lowering the tv, and moving the mains to the sides of the tv. Any pics of the back of the room? Might be able to help think of some way to place surrounds.