I can't hear anything coming out of the sub at 40 Hz.

I agree with your last paragraph: "BTW, you want to hear all of the music out of the sub, to a point. It sounds like the crossover in the sub may not be working--does the sound change when you adjust it? At 40 Hz, you shouldn't be hearing anywhere near all of the music."

Polk says to send the DSP board back to whence it came.

Eric G.