I don't know about P5 (no Mac version), but it's straightforward with P4. Export the obj (convert shaders to jpeg) to its own folder, which will contain all the shaders, the obj and the mtl file. Then Poser reads the mtl file to get the shaders list. You may have to use the Group Editor to spawn props and rename/re-assign materials if they don't show up right after import into Poser.