First of all, there are SuperFly textures for the HiveWire Horse. I just checked my PP11 Materials Library, and I have 2 folders, one HiveWire Horse, and the other HiveWire Horse SF. The .mc6 files in both are dated back in March of 2016, so have been around for a while. Check and make sure you have them as well.I agree, the superfly has potential but the horse textures need some work, mainly I think with specular which superfly struggles with using some firefly materials.
As far as specularity goes, SuperFly doesn't use specularity, as it's built-in to SuperFly, so you can try unplugging any Specular nodes from the PoserSurface, or just set the Specular_Value to 0.0, if you want to render in SuperFly. How well that would work with the HW Horse, I don't know as I haven't tried it.
There's also the CyclesSurface and PhysicalSurface Root Nodes you can try for SuperFly renders, though the PhysicalSurface node is a lot less work to deal with, and it does have a node for Specular.