Deej Mixer
Deej is an open source project that allows you to use physical sliders to control windows volume mixer. I did not create the program but I did make my own version using the existing code. My version Deej uses 7 Sliders with a mute button for each and 7 additional function keys that simulate F13-F20. One thing I would do differently is that I would make each mute button cut the signal wire rather than connect the signal to ground because when the slider is muted while at max volume there is a nearly 0 ohm short to ground.