HI 
I’ve never heard of face shift,. i’ll check into that later,. but right now I can explain a couple of things.
Daz figures only have a couple of bones in the head ,.. there are several in the tongue parts of the Generation 4 (V4 . M4 etc..) and the same in the Genesis figures. but less in V3 / M3 etc.
Facial animation isn’t normally done in Poser, / Daz Studio, or Carrara by animating Bones, apart from the Jaw and tongue, and sometimes the eyes.(although it can be, ..if you’ve built the figure that way)
Most of the facial and Lip-sync animation is done by adjusting morphs in the figures head.
you’ll find that even the Base figures have a bunch of “Viseme” morphs, ,.,shapes for vocalisation, like Aa, Ooh, Ch, etc…
You’ll also see some basic facial expressions,. like Happy, Sad, Afraid, etc…
All of these morphs can be animated to produce the facial animation you need, you can make the eyes blink or flutter or wink or wince.
and as with all animation, you have keyframes and tweener types in carrara which can be adjusted to suit what you want.
There’s also Mimic Pro for Carrara, which is a Plugin, to create Lip-sync animation from a vocal ,..audio (.Wav / Aiff) file.
In Carrara 8 and the 8.5 beta,.. you;ll also see a thing called “Puppeteer” which is also in Daz Studio,.
Puppeteer allows you to create a bunch of (Pose) dots in a grid, where each dot represents a different pose,.
you can then run your mouse around over the dot’s, and the figure changes as you move.
you can record this as an animation,. whether the pose dot’s you create make the figure Walk, Dance, or only change the expressions of the face is up to you.
Lastly,.. BVH files,.. I love them and use them all the time BUT… they have some issues.
Normally the BVH is a list of Bone names and XYZ locations, and that’s exactly what it should be.
but BVH are specific to the figure they were created on,. (because of that “Bone names” list)
this means that unless the figure you’re applying that BVH to,. contains the exact same names for all the bones,.. you’ll either get Nothing,. or an error,. or a completely distorted figure.
To load a BVH onto a figure in Carrara,..
You need to select the HIP bone of the figure,.. then go to FILE / IMPORT, then locate your BVH file.
but because there’s only a couple of bones in the head, you may only get some head motion, rather than a range of emotions.
Hope that makes some sense 