OK, I actually built a volume control similar to the one eTronics sells, using the following RadioShack components:
-Stereo Volume Control Potentiometer (#271-1732) $3
-Headphone Extension Cord (#42-2562) $6
-Control Knob (#274-402) $2
Split the cord in half, strip wires, solder wires to pot, and you're all set!
I can post some diagrams etc., but what I did is not too different than what OscarControls has at:
http://www.oscarcontrols.com/volumeWhat's so nice about this solution, is that you don't have to tamper with your existing speaker wires etc!