Thank you, Hborre. That's helped.

I cannot find BSDF in PPro_11.3, but I still do not know more than a fraction of the 'advanced' materials system...

FWIW, I found a much faster workflow within Irfan View for manually extracting and saving Alpha channels. Applying them to Poser test objects still requires negotiating a 'Grand Slalom of Gotchas'.

This 'bush' is one item from a 'Forest of Dead Trees' stage/scene MMD freebie posted by 'blackSoul1890' on DA. I ripped its PMX to OBJ+MTL. As the complete scene is too poly-heavy for convenience, I thought to mimic the model's extensive use of 'flats' for back-ground objects. Took some experimentation...

Using Poser primitive one-sided square scaled up, I applied the PNG (RGB+A) as-is to 'Diffuse' (100%) and 'Bump' (0.10). 'Highlight', 'Ambient' and 'Reflection' must be set to black to prevent untextured parts of the square 'ghosting' at certain angles. The Alpha channel file went to Transparency (100%).

Superfly test render ran okay. I replaced the bush and bushA pngs with grass1 and grass1A, and that worked, too.

I'll save out as OBJ+MTL, study MTL using 'Notepad', add appropriate 'Transparency' calls to original scene's MTL. As ~40+ such calls, it beats navigating 'Material' menus...