I've only hooked up the one and it sounds great. I'm waiting for a y connector to get the other one on line. It definitely improved the performance of the Polk M20s. Now I have EMP E55Tis and they sound even better. I don't think I'll experience the full impact until I have both subs connected and watch a movie with some serious bass.
Great. Congratulations on your new subs, I'm sure when they are both hooked up it'll be even better.