Just a silly suggestion, but... have you considered using normal maps, in addition to bump, specular and displacement maps? It's something I learned (the hard way) to do, whenever I have to move models from, say, blender, to Poser, or DAZ. Because the shading used is so drastically different between software, normal maps are a sort-of "universal" method to tell the surface how to react to light, in refraction/scattering and reflection, as well as adding up some additional pseudo-geometry detail. If you don't have premade normal maps, but you have photoshop, Nvidia has a photoshop plugin that makes normal maps out of diffuse ones, and, you can even add your bump, or specular, or displacement map, to add extra "detail" to the final result
