As mentioned above XTZ aren't sold in my country and import duty is extremely high that is something I may not be able to afford. I did ask a Polk seller (trading in with an another Polk sub which I am not a mood to unless the deal is great) he said he would buy it at $250-260.Another thing even if I get an XTZ sub, there won't be any after-sales support incase in the future something goes wrong with the sub.12.17 would be best for that room, but the 10.17 might be more budget conscious and you only give up a small amount of bass extension and ultimate output level (which you can't use anyway due to neighbors). Place it nearfield (as a side table or just behind the couch), for greatest impact at the lowest gain setting.
Sell the Polk and add the proceeds to the sub fund.
Have you checked Klipsch SPL-150? That is something I might consider something down the road if I were to stretch my budget ($1500 vs $1900 PB2000 Pro). Do you think a single SPL - 150 would be enough for my area (4000 cubic foot).