I am trying to use the other .nvf files included in the “models” folder after you install the Maxine SDK but they both do not work when used in the Face Track CHOP / SOP.
Specifically the “face_model3.nvf” file since it includes more expressions than the default Surray model.
Currently it seems the only was to get expressions is to compile a custom C++ CHOP based on the SDX FacialExpressions Example? 
Sorry for the delayed answer. I think those face models are from the 0.8 version of the SDK which doesn’t seem to be compatible with the 0.7 version that is used in the current 2022 official TouchDesigner release.
In the experimental 2023 release we have updated to the latest SDK and I’ve confirmed the face_model2.nvf file will work in our next update (there is a different bug that blocks it in the 2023.10130 release that came out last month).
I believe face_model3 is only for expressions and as you’ve noted we don’t currently support that feature. It may be something we add in a later release, but its not on our timetable at the moment.