Hi Tony,
We are very sorry for the very late reply. The forums are still not very active yet and we have not been monitoring them as closely as we should.
Regarding your question, you are correct, the Migrator does not currently allow selection of Forums to migrate.
However, you should know that the limit in the number of forums is a licensing limit, not a physical limit. You could migrate all of the forums and then through Community Server's Control Panel, move posts from one forum to another so that you don't lose any posts. You could then remove the empty forums to fall back to the licensing limits.
I don't remember if Snitz has the ability to move posts, it probably does, so that could also be done before migrating, that would be up to you.
I hope this answer helps, and again I'm terribly sorry for the late reply.
Michael Trefry