The real issue is that the PoserSurface Diffuse_value is wacky.  To match correctly with IDL, you would need to set diffuse_value to 0.15 on all materials. Not very practical.   The work around, either set the material diffuse_values to 0.8 and increase your lights to 800% with IDL or set the Render IDL Value to anywhere between 0.1 to 0.3 from the default 1.