Can I ask what file did you use from zbrush to CNC software. Obj. or Stl.
Hi,
I mostly use .3dm now, just because Rhino can mix obj-fbx and CAD data. As for the nurbs it is only important when you use more than 3 axes machine. With nurbs you can calculate normals to keep the cutter perpendicular to the surface. This is important for smoothness of course but not too much for this kind of models.