The problem with the Wavefront .obj file format is that it was created years ago, and doesn't store all the material information you need.

Back in Poser 4, the only thing we really had to worry about losing was transparency and transmaps. Poser 5 adds dozens of new material settings, including the infinite combinations of shader nodes and procedurals, and there is no way to put these in the .obj and .mtl files.

In the past, I've gotten tricky by first saving the scene as a .pz3 file, then exporting the elements as an .obj file, reimporting the .obj and saving it as a Poser prop, and then finally manually editing the prop file, cutting-and-pasting the material section from the .pz3 to the .pp2.