The first thought is Gamma correction.  It doesn't exist in P6 and unless you modify your shaders to take Gc into account, the comparison is not exact.  Also, your lighting is much more intense than your PoserPro post.  Believe me, as a scientist, to make a valid comparison, everything must be equal and optimized straight across the board to obtain significant results.  I would examine render settings, material settings and shaders, and set lighting equally for all media.