I just stumbled onto this URL, which describes a way to make a very
simple 4- knob fader box that plugs into a joystick port. There's no
reason you couldn't use slider pots instead of knobs...

http://www.univ-lyon1.fr/~jd/groovit/Jbox/new.html

In light of recent surround-sound discussion, I thought this might be of
interest to folks on the list.

Best,