That is: Original File -> Wave Parser -> ffdshow -> wav dest -> file writer (.ac3)
ffdshow can now encode to AC3? My Google-bility is weak... where did you find the filter you've labelled as "ffdshow"?
Does anyone know how good ffdshow/ac3filter are at AC3 encoding compared to, say, just off the top of my head
Sonic Scenarist's AC3Enc?DE
PS From what I've read encoding requires the newer, somewhat unstable version of AC3filter.