i dont think photoshop 3D thing (?) supports any material files, since materials in diffrent programs usually are very unique, the mia_material_x (for example), might not be supported by any other 3D program. what you need to do instead is focus on maps like specular, diffuse, transperency etc. I dont see why you need your shading network to be imported in photoshop, since photoshop is mostly 2D i dont understand how you would get your shading network in there ?