The problem is the smallish sub. That system comes with an 8" woofer and 100 watts of power. You aren't going to get a ton of bass extension with that sub. Also, if you are trying to fill a big room, you'll run out of power.
I'd make upgrading the sub a priority. There are some decent choices available for a few benjamins from HSU, SVS, AV123 and others.
Jim