Thank you for this thread. I've learned a lot.

I've come to OBJ texturing via porting a bunch of 'other' file-types. My 3DOC ($$), Open3ModViewer, Noesis, Irfan View, XnView, XPS>>PMX, PMX Editor and D3D's 'DSF Toolbox' ($$) are kept busy. I've recently converted several DS scenes' multiple props from DSF format. Though 'Toolbox' usually handles DSF meshes okay-ish, it does not export even a 'basic' MTL companion file.

Sometimes OBJ materials match texture names, sometimes there's few enough to figure.

Happily, most DSF & DUF files may be 'un-packed' using eg 7Zip, then the un-typed file within opened as 'indented text' with eg Wordpad. Basic texture calls live near the start of a DUF, but there's also much MC5/MC6-level detail to trawl. Looks 'Advanced Material Room' stuff. At least Wordpad lets you search for textures by name or file-type suffix...

Now that DSON is officially deprecated, if not dead, would be nice to have a utility to rip DUFs to both MTL and MC5/MC6...

( I have DS but, like Blender & GIMP, I cannot grok the UI... )