What I am trying to do is setup a network, in which all users belong to a main site, but then can join a sub-site (preferably one). I have looked into the BP Multi Network and BuddyPress Multi Network plugins but I am not sure which one would be better for what I would like to do. I would like to use a sub-domain setup of multisite along with buddypress. Everyone would sign up through domain.com-which would just be a sort of hub to all the sub-sites-and then be able to join the specific sub-site to which they should belong. (So if they were from Ireland, they would join ireland.domain.com, and not be able to join england.domain.com.)
I know this is a kind of complex question but the multisite buddypress combination is pretty confusing, and any help at all would be much appreciated.