Quote - To my eye, everything is different in those two images, not just the specular. The whole image is lighter, apart from the background.

Perhaps it's to do with the fact that Poser is 'combining' everything in linear colour space and then gamma correcting, whereas in Photoshop you are combining individually gamma-corrected passes.

Possibly?

thats because of the specular.  the diffuse is the same. 

you might be right and its really the GC. but how to fix this now?