If RGB is all you want, then I'd suggest this:

http://www.amazon.com/dp/B00988GMLG/...I3E7KCFRJ0DUTQ

Upscales RGB to HDMI, so long as you have a region-free cable. ProjectCOE.com and his youtube channel have a good video on it walking you through everything to ensure a trouble free setup. Witghout modding, the Genesis can output RGB so you should be good to go from there.

Edit: AFAIK, all Genesis models output the same RGB output. It's the SNES that has the RGB variations moreso than other systems, but I haven't heard much in terms of Genesis.