Just built a new FFMS that supports 4:2:2 and 4:4:4 videos, you can download it at:
http://nmm.me/kx
I tested this version using a
DNxHD sample posted on
this page. Seems it works correctly, the LSB part come out without problem. AvsP incorrectly reports the clip as YV12, subtitle("IsYV16: " + string(IsYV16)) shows the clip is actually YV16.
Hope this helps.