hardware...

I'm curious, can anyone describe the differences between the pc engine
duo, duo r, and duo rx?  It'd be cool if there was a "hardware" page to
go along with the "games" pages on the list site, that had pictures and
info about all the different pc engine/turbo grafx pieces of hardware.
I've seen some pretty wild stuff on ebay that I never even knew about
before (like the "print booster").