[I think] JROK doesn't work or it's not known if it works with a Turbo Duo and that's with or without the separate Sync cleaner. And JROK is your only professionally made kit so far BTW... Up to you if you wanna take this risk.
I do know of something that might be better down the road from a guy called Ace if you're willing to buy and install a IC chip or two, but it's still in the development stages just like the circuit that steve is working on in my thread that was linked above...
http://www.sega-16.com/forum/showthread.php?22237-New-RGB-to-Component-converter-design-using-the-BA7230LSThere's a chip called BA7230LS (you can buy it from utsource.net) that inputs RGB and outputs Luma/Y, Red-Y and Blue-Y, however, it doesn't mix the Sync and Luma for you so that's done externally, but he's had problems doing that on most systems... On a Turbo Duo, he said it works good with the LM1881 chip which strips Sync from the regular Composite signal which works out better when mixed.
Anyway, you need to become a member of the Sega site to see his circuit and maybe you wanna ask him for more details, but yeah, his circuit is still in development, he's still learning that chip and it not mixing the Sync has been a problem. That much I know. So basically, the sure-fire thing here so far is S-Video, and when it comes to Component mods, you need to wait a little while longer, but we're getting closer.