It doesn't seem to do what we need, though I'm not technical enough to say so with total certainty. I understand that another site is using PHPBBS to do what I want to, and am trying to speak to their owner to find out how, so far without luck.
The issue is that there will be many threads in the Forum, each one needing to be private to just one user and the mods. Could end up with hundreds of such threads over time, so I am trying to do it as cleanly as possible, if that makes sense?
Thanks for all help!