I've just had my Wii modded with Wiidual. I'm only interested in it's analogue signal as I'm using it with my NEC XV29+ CRT . The signal chain is: Wiidual -> Extron 203Rxi -> NEC. The Wii's connected to the Extron using the retro access Wiidual csync RGB scart cable, which they altered for me so that it has a VGA/DE15 plug instead of the scart plug. Then the Extron outputs to the monitor via the official Extron BNC to DE-15 cable.
I have a couple of problems. One is that although an image can the picture will occasionally blank out and sporadically flicker as shown in this video:
https://www.youtube.com/watch?v=7JaAI4L2zeU
This happens when first powering on the console and also here and there - often when there's a screen of pure white.
The other is that there is a kind of wavering around the edges of some contrasting colours as shown in this video:
https://www.youtube.com/watch?v=WGUR8Hxj768
It looks more prominent in person.
I know that the NEC XM/XV/XP monitors need a sync stripper for 15Khz scart - could this be the case here as well? I don't know enough to be sure, but I was under the impression that the Extron should take the RGB signal from Wiidual and output RGBHV with the correct HV sync for the NEC. The NEC works fine with my Gamecube + VGA modded D terminal cable via the same Extron, so I'm not sure what the problem could be here.
Also, the odd thing is that I only get an image with the correct colours when I set the Wiidual to RGsB - sync on green. This seems a bit odd to me - Setting it to RGB gets only occasional flickering. The only way to get the right colours is by setting the Extron like this:

Down is off. Oddly, 'mono audio left' has to be on to get an image. I'm guessing this has to be something to do with sync. Do I need to get a sync stripper in the chain? And if so, where should it go - inbetween the Wiidual and the Extron, or between the Extron and the monitor?