Old topic but I ran into this problem aswell, was looking at the cores used from the associated cores and found one "Genesis GX Plus" which was assigned to both but dropping down there was also a "Genesis GX Plus SMS" so using this you get two of the same core = separate control mappi g and bezel for the core. Don't know if this is a lunchbox feature or RetroArch, didnt found anything about this SMS version on Google. Works great though