If you want it louder, go two subs. You can get a sub that is double the power but to the human ear, it won't sound twice as loud. If you want it louder, go the Kicker Comp C12 subs in a box and get a monoblock that will run around 300-400rms. You'll be more than happy with it for sure. Don't bother buying another single sub and a new amp and expect to hear a big difference.