headphone jack built into the controller. That would be one heck of a hack, don't think that is possible on a Turbo Duo. The NES didn't have audio in the cable, do you have pics of that? But I suppose I could run that headphone cable along the controller cable, and then just extend it to the headphone jack (for the Duo users, the TG-16 didn't have that feature correct?).
Cool idea but I could do that with a SNES controller (have my cake and eat it too).
Sega Genesis 6-button, I am going to have to side with the Saturn vote, but to sacrifice the Saturn pad would be sacrilegious...