I imported it into 990, and it worked fine the first time! I know about having to tweak the .sml file, and I still had to do that with 990 (two sided, alpha transparency, etc.), but it showed both materials!
There's a very good chance that I may have messed up my attempts to import into 980 the first time, and then never cleaned up all extraneous files — I think it's time for some house-keeping in the addons folder...
SIncere thanks for looking into it, I really do appreciate you taking the time. I shall page you when I have some screenshots ready.