I installed a compact Kicker 11HS8 150 watt subwoofer with my new 8200 unit.

The subwoofer is self-powered and connected to the h/u, and I also have a separate amp that is powering the four speakers.

However, the subwoofer is very under-powered, even after I set the filters correctly.

I have to lower the speakers to -24db and raise the subwoofer to 10db just to get it to marginal levels.

Is there anything else to try, or is this subwoofer just too under-powered?

Make sure that you have the input level switch on the Kicker set to "Lo". Also make sure the gain control on the Kicker isn't all the way down.