advanced rendering for AutoCAD
For AutoCAD I don't think you need to manipulate this-- leaving it alone should work. It's there for other applications (Rhino, Sketchup, etc.) which permit multiple sets of texture coordinates on the same mesh-- native AutoCAD doesn't really support UV texturing at all.
A further question: What is a solid texture?
Currently only one texture per component and one bump map. There is a blended material which allows more complex permutations-- most people do texture blending in photoshop.
Solid textures refer to the granite/marble/wood procedural textures. They're now lumped together-- you can choose a procedure in the interface.