Look out, qwesome article about dreamcast RGB mod with the ArcadeForge's UMSA. Again from VideoGamePerfection. :)
I recommend to put the SLG3000 between VGA Switcher and Display VGA Input :D
Umsa meets SLG3000 ... okay almost.
I don't know please help me. Sometimes SLG SCART is used for descaling 480i to somewhat what yould look like 240p almost. So in this setup between UMSA and Display SCART Input a SLG SCART could be used.