The first thing I'd like to point out is that as the Principled BSDF is an individual node it is easy to blend between multiple materials using a mask. The setup below is very simple but the concept is the same no matter how many materials and masks (procedural or image-based) are used.

Two complete materials are defined; a mask is defined using a Poser Tile node; a Poser Blender node is used to tell the render engine which material to render according to the values taken from the mask (a Cycles Mix node with the mask plugged in to the Fac chip could also be used).

(This scene uses a black material on the Background material zone of the Poser Ground, and a mid-grey on the Ground zone as I want to keep bounced light way down. There are two area lights, one in front and to the side, and one behind the prop. The prop itself is a simple rounded cylinder I made with a couple of levels of render subD applied.)

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