dont export the really high poly models from z straight back to Maya. The idea mentioned is that you build the basic form of the model in Maya, and then export that to Zbrush. Then you can subdivide it to sculpt it at higher polycounts. If then you want to bring that back to Maya, you can use normal and/or displacement maps to try and carry back the high resolution detail from Zbrush, while having a low enough polycount model to not cause problems for Maya. Try having a search for 'Maya ZBrush Workflow' on google.