Else discover the speedy Blender (free) Method! (with some hairs losted...this prog is a mess) :)

Import OBJ (no "Marching cubes" ) from MagicaVoxel : Select the Object ..Edit Mode / Face .... Press F
.
that all : triangulation is gone ... you can export ! :)

_importOBJ by Max Smirnov for MOI
You have a solid (no subdivisable) perfect for nurbs operations!



Some moments of inspiration later! :)