High amperage High-pass filter

How about a line level EQ? What is the setup? Source - Pre amp - power amp?

Contact Parts Express -- they should have what you need. Here's the link:
http://www.partsexpress.com/

What would be a good source for learning how to assemble the needed caps, inductors, etc?

Line level will not work for this particular installation.

The set-up is music server-> integrated amp-> speakers.
The speakers are on the "A" tap and the subwoofer is on the "B" tap. This way they can turn the sub off with the touch of a button for low volume (less crowded) times. The problem is that there is a huge peak in the bass of some of the music they are playing around the crossover point of the speakers which causes them to bottom out at high volume levels.

Thanks for the link!