I vote for the US Duo and Supergrafx or Core. Like folks said already, a US Duo will run your US Hu's and all (S)CD's and the Supergrafx/Core takes care of your few JP Hu's. I would go with the Core because at the end of the day, there is not much for SGX and the two games you WANT, will set you back. Plus the Core is pure sex.
I un-region locked my JP Duo to work with my Kisado. Before the Duo, I had a TG-16 CDROM w/ ACD but it finally died (donation to BlueBMW!). With the convertor, it played everything except SGX but it seems convertors are getting pricey.