I always check flip the normals when I export.
I don't understand how to duplicate the faces unless you mean export with it checked, then export with it unchecked.
I don't have access to 3dsmax now, I'll try to explain it to you from how I remember it.
Object QuadMenu (right click on the object to export) -> Convert To -> Editable Poly
Then select your object, go to the Modify pane, click on the Editable Poly modifier, then in the rollout select Face editing (that's the red 3D square). Then CTRL-A to select all your faces, copy and paste. (If it pastes to a different object, click Add in the Modify geometry group, and click on the newly created object) With your new faces still selected, click Flip Normals (int the same rollout somewhere).
Now every face is duplicated, one with it's normal in the original way, the other one with it's normal flipped.
Export it now, however, mind that it has twice the vertices as it had before. It's a very dirty fix.
