Sorry. I wrote that just before you posted the images and description of those character rings. For something like that, i would do as Michael suggested. Model a single surface Nurbs shank, export as quads to Silo, then add extra geometry (extruding, spinning edges, etc) to build the basic volume of the face. Then sculpt the fine character details...

In a general way (and reading a post about using Silo/Moi for architectural purposes), then i suggest roughing out a shape in subd. Since you also have Rhino you have a another set of excellent mesh refining tools. So you could easily boolean a Moi mesh together with a Silo mesh, then use Rhino tools to adjust the transition area. Or even send it backwards to Silo again for smoothing with the sculpt tools...

jonah