I haven't used Keyshot but if you're not having a lot of luck generating PBR for it, you could try using the suite's "Last Gen" option to generate the old school specular setup.
I just found out how to use pbr materials in Keyshot. All you have to do is use material editor to plug in your diffuse, normal and roughness map. You don't need the metalness or metallic map because you can drag a keyshot default material on the model to simulate the metallic map. Just hold the alt key to retain textures…