No need to waste an extra modifier on this
-select your object
-go to the Modify tab
-in your stack, there should be an editable mesh
-select polyon sub-object mode (red square) or hit "4"
-in the edit menu : "select all"
-move to the bottom and hit auto smooth
-your smoothing groups will now recalculate according the mesh topography
just go out of sub-object mode again.. and you're done.
@darkslayer
All though the smooth modifier works also, you should take the habit to never leave a stack intact and always collapse it back to an editbale mesh.