need help to replace my subwoofer

Hi,

I bought my HT one year ago and I believe I did a mistake on the subwoofer. So I'm now trying to fix it. My dailly usage is basically TV/Movies and games

Here are my current specs:

- Room size: 3500 cu ft - TV area is just half of it.
- sub located on the corner
- receiver: Onkyo HT-RC270
- Speaker settings: 5.1

These are the speakers
- Center: Polk CSI A4
- Front: Polk RTI A1 (bi-amp)
- Surround: Polk RC80i

- Sub: PSW111
Bought it based on towns 5 star reviews on amazon.

Once assembled the HT sounded really nice except for the bass that really sounded crappy even compared to the last HTiB I owned previously. The original settings got from MultiEQ had the crossover settings on 80Hz, I increased it to 120 and the sub sounded a little bit better but also crappy.

I'm looking for a replacement to solve this issue. However I have basically 2 limitations:
- Budget : up to 300, but I can extend it to 400 for something really good since I'm planning to keep the sub on my next upgrade.
- size: The sub must have up to13.5 width otherwise it'll not fix on the corner and my wife will gonna kill me... So I think most 12'' subs are out.

I've reading reviews on several places and saw the supercube iii but I believe This one will not sound much better than the PSW111. Also considering DSW PRO 500, however I was thinking on leave polk behind.

Anyone has any suggestion for sub to replace my psw that is on budget and on size?

Any help or suggestions are welcome.

I was checking the RW-12d but this 299 promotion is not valid anymore. It is being selled by 499. Best price I found was amazon with 379 + shipping.

What about the "Klipsch Sub-12HG Synergy Series 12-Inch" I saw it on Amazon by 299

Any suggestion on Definitive Technology? The proSubs are thin, even the ProSub1000 will fit on the spot I have. The question would be "is it worth?"

Thanks