I use a rig of head bones to make expression. I have a workflow ready from max 9 to MED by FBX. I have used although the 2 Parts solution of impaler, but the 2 models never move in the same frame... So the head was always following the body a little bit later...
Another problem with the 2 parts solution are the seams of the both parts. They are not smoothed.

Kind regards

taratoga