Physical Surface root will work with Firefly, to an extent. I've set up props with PBR textures and got similar-ish results from both engines. Bear in mind the big difference between the two - in Superfly there is no specular, only proper raytraced reflections on everything. If you use Physical Surface root you also get fresnel reflections automatically as well. With Cycles root you'd have to add it to everything manually.

I tend to use PBR Metal/Rough workflow, which is easy and and compatible with lots of other render engines (including Iray) and for that the Physical Surface root is pretty much plug and play. For materials needing refraction, translucency or volumetric stuff I have used Cycles root and surrendered the preview (which could be an OpenGL issue?) - depends on the material. (I have found that if I make a material that doesn't work in Poser's preview I can make a simpler material using the Poser root, set that to Firefly only, and then whenever the render engine is set to Firefly and saved in the Render Settings it will preview using that. Switching to Superfly and rendering resets the preview back again. Fiddly, but a sort-of workaround.)

Shameless self-promotion - the gun I made a while back was textured in Substance Painter, materials setup using Physical Surface root within minutes and this is a straight Superfly render. Superfly makes some things really simple now.

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