I'd start off simple, using not the inbuilt diffuse and specular channel - which does elaborate maths with each light in the scene - but a diffuse node (with the value set at .85 or so) and your texture map. Plug the texture map into the color channel of the diffuse node, and the output of the diffuse node into alt_diffuse channel of the main poser surface node.

That's where to start.

My desktop is down atm with a dead graphics card, or I'd put up some screenshots for you.

Lighting: keep it simple. One of the main issues with older materials is that they don't play well with the newer lighting modes, like Gamma Correction and like that. A simple material like the one above, one sun light, Iindirect Lighting and you should have a significantly improved render. Poser now handles internally what an elaborate node-kludge-set endeavoured to do in the past, with varying degrees of success.

But this is just the basic, basic beginning. From here, you can assemble an entire library of node sets offered for free by BB and others for most if not all of the main materials you'll ever need. Within the limitations imposed by the renderer itself - which are significant - you can render some amazing stuff.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks