My question is, has anyone done the opposite?
I have searched quite a bit, here and on Google, and it's hard to find an adapter or way to make an adapter to use a DualShock 1 or 2 or GameCube controller on an SNES (or in my case, a Retro Duo console, which has SNES controller ports). All of my searches seem to only find the reverse of what I want, which is also what most people seem to want. I know, I'm odd..
If anyone knows if a product to do this exists, I'd really appreciate a link. Or if anyone knows if I splice some wires from a DualShock or GameCube extension cable to the cable from one of the Retro Duo controllers, if that would work, your input would be appreciated.

