It is my understanding (thanks to alpac) that the cross-overs are located in the amplifier. Is the cross-over on the input side to the amp? For the mid-bass speakers in the doors, is it only a low-pass filter? Now that I have a sub-woofer I would like to add a high-pass to eliminate some of the bass that the door speakers cannot handle very well. I'm thinking I could add a passive filter on the output of the amp. I believe that the speaker are about 6 ohms. If I use a 300-400 uf cap this should give me a 6db/octave highpass at about 75-100 Hz. Am I on the right track here?