Or, you could just buy an SVS subwoofer and call it a day.
http://svsound.com/products-sub-box-pb12nsd.cfm
I've never heard one of their box subwoofers, but if they're half as good as their cylinder subs, you'll be very, very happy. Not to mention the excellent input/output options and actually functional and useful crossover and phase controls. Yes, I acknowledge that I am recommending a subwoofer that is twice the price of your actual speakers, however, this subwoofer will last you forever and has enough power to be used anywhere...ie if you upgrade to a large speaker setup down the road, this will still be useful. Also, the Daytons are a lot more pricey than they used to be. You can spend more on a Dayton than on the SVS at this point, and they don't even come assembled! I haven't heard a Dayton, but the likelihood of it being as good as the SVS...I can't say, but SVS has a very good reputation and after hearing some of their products, I'm rather sold on their quality.
Edited by MD1032 - 10/15/11 at 4:24am