I had SFII CE for my US DUO, before I got a Duo R I used to use two different Converters that allowed for japanese games to be played on my US DUO.
I had the Kisado and a long green diving board. The Green Diving Board I got from TZD back in 1994, they said that it was mainly a test model and wouldn't last very long, well 13 years later........
Since getting the PC Engine Duo R I parted ways with the Kisado, but kept the Green Diving Board. Mainly so I can switch Game Data Between my US Duo and my Jap Duo R. I had my friends stumped on how I had saves for Order of the Griffon on my Japanese Duo R without a MOD job....LOL
Anyway, SFII never worked on my kisado adapter, but worked perfect on the Green Diving board. Strange eh?
Sorry for the converter rant........