The RX/R has the better main board. The CDROM drives are the same. Whoever gave you that info was full of it.
Techies have reported black Duo's having better mainboards, it's just the caps that are shitty:
the tg16 and duo-r are build on low end non critical use only boards, but the black duo (US and JP) are built an aircraft grade materials (except the SMD aluminum caps)
These are the pros and cons as far as I can tell:
Black Duos: headphone jack, best mainboard / worst capacitors, lens tends to jam on CD-Rs
White Duos: better caps, fixed some heatsink issue / cheaper components otherwise (although this hasn't caused any widespread problems that I know of).
Black PCE Duo: half the price of a Turbo Duo.
IMO, buy whatever you want. These things are all twenty years old. Any model is a crapshoot.