**Dealer disclaimer**
I don't think you are limited to a sub that small. Thats not to say you can't get good results from them though. I would think a good quality sub of 12"-15" would be fine. My main room at home is 16X20, and I use a pair of 12" Velodynes for stereo. I also have an 18" Velo in that room which I add for home theater. The JL's are great too. You didn't mention a budget, but the PSB's are real musical, and a lot less money. If I ever go with new subs, they would be on my short list as well.
I don't think you are limited to a sub that small. Thats not to say you can't get good results from them though. I would think a good quality sub of 12"-15" would be fine. My main room at home is 16X20, and I use a pair of 12" Velodynes for stereo. I also have an 18" Velo in that room which I add for home theater. The JL's are great too. You didn't mention a budget, but the PSB's are real musical, and a lot less money. If I ever go with new subs, they would be on my short list as well.