I wonder, then, if it's the fact the facets are triangular. The shadow I get from a DAZ Studio figure and clothing looks right to me. The poly count is 100,000+, but most are quads. I'll try with a small converted STL later today to test. I have an 11.2 million triangle/660Mb model I could try testing with after that - will be fun , but I have no expectations of it working, and had none for DS, and was pleasantly surprised when it did work.
I was impressed. Imported the 11.2 million facet model, and while it slowed the machine down, it was not a jerky as I had feared. The model represented 3 man-years of design work and crippled the same machine when in SolidWorks (15 minutes to change view degree of crippling). Now I only have to work out how to texture map such a model & I could do some publicity shots for it as opposed to our usual CAD drawings. That'll surprise the boss..