I believe the SNES and NES pads are very similar. I also believe I read that you can mix and match SNES pads and NES pads on the 1 parallel adaptor. Wire NES pad 1 to db25-10 and NES pad 2 to db25-12 and SNES pad 1 to db25-13 and SNES pad 2 to db25-15. The you just have to set up controller 3 and 4 to use the SNES drivers and controller 1 and 2 to use the NES drivers. (In the game controller panel) Should work like a champ. (Just so you know, I haven't tried it myself, but like I said, I believe I read it somewhere about the mixing of the 2.) Good luck.
J_K_M_A_N