Thats kinda tricky you want your poly surface to be as light in geometry as possible. Remeber the a low poly cage once coverted to sub-d is usally pretty smooth. The trick is working in the low poly cage to add detail but keeping the sub-d geomerty low once converted.

I have my settings for going back between the 2 set as

Subdiv to polygons:

I have vertices checked only. This setting allows to covernt back to polygons at its lowest geomerty.


Polygons to Subdiv:

just use defalt if need be you can up the base mesh from 1000