Powered subwoofers. I have a Klipsh 10" wired into a selector for TZ, JD and STTNG (one side of my room). Basically, I just press a button and it switches to whatever game I am playing.
On the other side of the room I have a 800watt car amp powering a 12" infinity sub hooked up and powered by a computer power supply... it's loud. I had a Polk Audio 10" on that side but it was too weak for my taste so thought I'd try my car sub.
Might make a topic to about setting up multiple machines to a single Subwoofer via a selector since I think several people are under the assumption that they can only have 2 pins to one external sub (2 channels).