[HELP] AviSynth 32 bit - ColorMatrix filter not working for video?

[Selur]

from doom9s answers:

It's the expected result, because you used 2 different ConvertToRGB32 matrices

Source was converted to RGB with 709
SourceFiltered was converted to RGB with 601 . Normally there would be a colorshift , but you compensated for that with colormatrix Rec.709->Rec.601

so question is how does the preview code needs to be adjusted?

instead of using two different matrixes, like I did:

SourceFiltered = SourceFiltered.ConvertToRGB32(matrix="Rec601")
Source = Source.ConvertToRGB32(matrix="Rec709")

Should I use both times use:
ConvertToRGB32(matrix="Rec709") since I specified it as 'from' in ColorMatrix
or
ConvertToRGB32(matrix="Rec601") since I specified it as 'to' in ColorMatrix
or
ConvertToRGB32(matrix="Rec709") since I specified it the source was flagged with it.
?
I suspect it '"Rec709" since I specified it the source was flagged with it', but I'm totally unsure atm.

Cu Selur