Just using Avisynth/MEcoder "should" use ffdshow, but it will depend on how you have the codecs set up so play on your pc.
To get ffdshow to upscale you need to set that in the options of ffdshow.
take a read of thishttp://ffdshow-tryout.wiki.sourceforge. ... %26+aspect
However after more testing I still gets a lot of stuters with upscaling this way (ffdshow/avisynty)
I still find using that beta with the mecoder upscaling to have the best perforamce, any chance you could change that back to how it was in the beta shagrath?