A subwoofer is designed as a supplement for most speaker systems to cover the lowest bass notes. In a surround system, in most cases, the powered subwoofer (or LFE) is designed to add visceral impact to the motion picture. Look up subwoofer and home ...
look on ebay, i have 4 12" subs in the back of my dodge, i just looked up truck subs, and got 4 of them, all for 40 bucks
Is the subwoofer self powered? Many of the home surround sound systems are. If it is there is not too much you can do, but if it's not self powered by its own amplifier you could and one. Are you sure you didn't partially blow the subwoofer?