I fixed my VSFilter issue - I had to block several filters: Arcsoft Video Decoder, Cyberlink PDVD8 h264 Decoder, CoreAVC (it has trouble with AR on some videos), etc. and chose FFDShow as the decoder for the target videos (x264). Now it can connect! Naturally, VSFilter is limited by the resolution output by ffdshow - if I leave the resolution untouched and let madVR do the scaling, the video looks quite good, but of course the subtitles are soft and/or jaggy!
I can't wait for the subpicture pin to be implemented in madVR!