Hi! I know this is an old thread but just wanted to thank you for the information as I was unsure how best to RGB mod my system and it was very hard to determine if the RGB output of the main console would work or if the Interface Unit would need the RGB mod.
I am a fan of non destructive mods so in the end I RGB modified my Core Grafx unit replacing the original 5 pin din socket with an 8 pin din socket leaving it backwards compatible with an original AV lead and no new holes required. I also modified my SCART cable to take the audio output from the interface unit RCA plugs giving me stereo sound as it was definitely mono returning via the IFU to the main system.
Well happy with the results! Looks and sounds awesome.