Two Subwoofer set-up in home - do they need to match?

I'm building a home theater in a large room (6000 cubic ft). I own an Axiom subwoofer. I'm going to buy a more powerful subwoofer (or two). Can I have one great subwoofer (that I will buy), supplemented by the one I already own? Or for true performance, am I substantially better off investing in 2 new subwoofers?