PCS should convert valid shields with no problem, just use modelview to be sure that they are there on the final model (and that they are the right size). In fact, that's all I use the PCS converter for now, as that's the biggest direct failings of the Max plugin is the ability to create stable and working shields. Anyway, all the shields that I've used that work (and that I can vouch for) are at most 200 polys. Their handling in both colission and rendering is a tad bit different from true geometry, so reducing your shield polycount is definitely something to try.