I guess I'll try the Cerwyn Vega, and if they don't work for me, I'll return them. Then I'll purchase a more powerful used powered speaker if it looks like I'm often going to be missing the extra volume that my KP100S isn't producing.

The Cerwyn Vega is on sale at Musician's Friend for only $150, and the shipping is only $12. Not bad for a 50lb subwoofer.

Beakybird