Re: Beyond me.
You're on the right track with the private post setting. But as-is, a post set to private can only be viewed by its author and by administrators.
But help is on the way. In the latest version of the software, just finishing its shakedown cruise, I added a hack to selectively broaden that access to various roles, e.g. Authors and Editors, on a per-node basis.
Bottom line, the next upgrade will let you set boards to public or private.
Oh, you want an ETA? This coming week, I think. I have to install it on a second university site first.