I haven't read the whole thread, but there are several methods for hard edges.

- When you import an X model with hard edges, you'll notice that the engine will display the hard edges too.

- You can create a specific hard edge between two polygons by separating them. This should not be a problem for stencil shadows as long as the the mesh has no 'hole'.

However I'll think over a comfortable solution in MED.

It's possible and runs very fast with *.X faster than *.3ds without the posibillity of smoothing groups.
But I don't know how this could be done.
I have made two screenshots of an example with a normal sphere (only the smoothing groups are modified). The sphere has 2 smoothing groups the upper half is group 1 the lower half has goup 2 and the left half group 1 and 2. All this is working in Quest 3D in realtime.

Here is an example out of 3D Studio Max:


Here is an example after export with panda X exporter and import it into Quest 3D with smoothing groups:

Oh!
I noticed the Vertex Count is increased. It seems that the Panda *.X exporter doubles the vertices on the hard edge to make it possible. Sorry this was my fault. There are no smoothing groups, but it works with all other features like stencil shadows, Pixelshaders...