Why are you "edit the AviSynth file and transcode the audio" when the avi is not PAL ? Are you converting NTSC to PAL ? DVD2SVCD sould do this automatically for you if you tick the box.
I've never done a 5pass encode (well not in the last few years ) to compare to a D2SRoba encode. But I've tested a 3 pass to Roba and couldnt tell the difference in final output, but I'm sure each each AVI will be different and give different results. The FilmMachine is great but D2SRoBa method is much quicker with better or equal results.