Sadly you are not likely going to be able to get big bass out of this system. Def tech seriously overinflates their sub responses. They list yours as having a frequency response down to 22 hz, which I doubt, it's probably more like 35-40 Hz based on my experiences with a deftech SC4000, which they rate down to 16 Hz, but it falls off a cliff at 30 Hz.
You can always turn up the surrounds a dB or two if you feel that they aren't producing enough surround effects for you.