Quote - 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.

How do I do that?

Quote -   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.

I saved the light setup in Poser Pro, copied and pasted the .ltz file into Poser 6's light directory and loaded the file in P6 before rendering.