Hi Defonten, when you subdivide in Zbrush I think there's an option for whether to apply sub-division smoothing or not. You'll need to have that unchecked when you do the subdivide since it's a regular polygon cage and not a sub-d smoothed polygon cage. I think it's a checkbox labeled SMT (for "smooth").

You can also increase the mesh density during the MoI export by using the "Divide larger than" setting as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2833.5

Also it's just a normal part of the ZBrush display that it shows things flat shaded so you can more easily see the polygon structure while sculpting. If it's that flat shaded look that is bothering you, I think there is a setting under display properties to do smooth drawing instead of faceted drawing for the display: http://docs.pixologic.com/reference-guide/tool/polymesh/display-properties/

- Michael