The right recipe is : set smooth shading to the object, enable Autosmooth (180° or whatever) then sharp edge on the edge you want. Export and voilà. I don't know about workflow in Xnormal. Keep in mind that this feature is quite new to Blender so if you have any trouble, contact mont29 or post in blender forum :)
I think I read it from @FourtyNights, in order to use auto-smooth to manually set sharp edges you need to use a 180 angle in the slider, like your image shows. The reason we do that is so the entire object gets set as smooth (except where you manually marked those sharp edges).
It seems to me that the Bevel modifier not having a limit to hard edges function is a deliberate design choice. I mean when you think about it, in a shaded smooth mesh, hard edges and bevel are oftentimes the opposite result in terms of smoothing. (And holy hell, is it just me or is this forum text editor really bad,…
@MACHIN3 What an amazing toolset this is! I'm on Max for a looong time. Learning Blender 2.8 for the last week and these tools are simply fantastic. I donated only $10, but will defiitely purchase your other tools even if I don't use them(which I'm sure I will) as it's always great to support lone devs who give us tools…