What is the absolute loudest subwoofer/amp package I could get for $600?

I am willing to spend around $600 for a subwoofer system of two subwoofers and one amplifier. But I want this system to be bumping very loud. As loud as anything around 600 bucks will get me. I am not sure what amp I have recently, but as for subs I have two JL audio W3's. They are loud but I'm greedy. ha , and I want louder. Any help on pointing me into a decision of louder subs would help alot.