Are you kidding me? That is the funniest thing I have ever heard.
Where did you base that statement on? Look at the port - there are 8 ports on this Duo-R. Look at a standard port - there are 5 ports. Hmmmm....3 extra data lines....and RGB has three lines.
How would one take composite and split into RGB? No - this Duo-R has RGB tapped from the HU6260 chip, and then fed to a 8din connector (note the 5 din connector has been replaced) - this allows you to use a standard AV cable, or a custom cable like you see in the picture that will allow you to use that RGB signal.
I can tell you that RGB compared to composite looks amazingly better, and no it doesn't actually look worse. I was going to do the 8din connector on my Duo, but this guy saved me the time. Worst case is it wasn't hooked up right, but I can take care of that.
That RGB adapter is only taking composite and turning it into RGB, so the end result is no better than composite.