If you buy a REL subwoofer then this connects to the speaker outputs of your power amp (it is very high impedance so it doesn't draw any power from your main speakers). This would fit perfectly in your system.
RELs are pretty good, but a bit expensive in the US ... a used Strata starts at about $800.
Any other sub manufacturer then follow James' advice above.
RELs are pretty good, but a bit expensive in the US ... a used Strata starts at about $800.
Any other sub manufacturer then follow James' advice above.