Specular in Cycles is not the same as Specular in FireFly. A spec map should not be connected to the Specular channel in the Phys Surface Node. There is a Gloss.Spec converter included with Poser that allows you to properly convert specular maps to Roughness/Specular inputs that the Physical Root Node expects.

For an example, see Included > SuperFly > PBR Skin Shaders > Phys Surface Node > LH SSS Spec Bump. 

The Gloss setting in that converter node will need to be adjusted up or down depending on how strong the specular map is. If the spec map is strong, the gloss setting will need to be reduced. The Specular color is set to 50% gray in the Phys Surface Node by default, like so:

One thing I do have to play with is which works better, adjusting Specular color in the Phys Surface node, or in the Specular color chip in that converter node.