I thought I would throw in my two cents. XRGB mini is great. I bought mine from SolarisJapan. Also I bought video cables from an ebay seller. They also sell SCART to XRGB mini adaptors. The ebay seller is retro console accessories. As for what type of RGB SCART cable I would say c-sync or composite sync. The N64 requires composite on sync. Game Sack release a good video types of RGB and SCART cables.
I currently have SCART for SNES and Genesis and JP21 on DuoR. I recently ordered Saturn SCART cables. I'm looking at getting a RGB NES. Also watching Game Tech US on their HDMI NES with Kevtris.