BuddyPress or bbPress?

I need some assistance from experienced users on this one. I know what functionality I need, but I am not sure how to achieve that functionality with a WordPress MultiSite Network… I cannot remember what all BuddyPress and bbPress do. I don’t even know if it is necessary to run both of them… Anyways, moving on.

My site consists of 1 main installation (which I will refer to as Site A) and X amount of children installations (which I will refer to as Site A1, A2, etc.). I was excited to discover WordPress Networks, since it allows me to accomplish this.

How I need the site to work:
I need the child sites to have their own STAND-ALONE social network and forum (BuddyPress/bbPress). However I do want the main install to have a GLOBAL social network and it’s own forum.

So I need a user to arrive at Site A and create an account. That account will need to be able to browse all of the child sites, participate in Site A’s social network and forums. The Site A account will also let the user create their own child site (optional). I DO NOT want the user with the Site A account to be able to create threads or participate in Site A1’s, A2’s or A3’s INDEPENDENT social network or forum until they have been added as a user to Site A1, A2, or A3.

That is where I am getting lost… I cannot figure out how to get these independent from each other, but still have a global social network on top of their individual networks.

I have come across the following threads that may or may not do what I need. Can anyone shed some light on how to do this?

http://ww.wp.xz.cn/plugins/bp-multi-network/installation/ – This plugin’s secription makes it sound like it deals with networks inside of networks. Not sure if this is one of the things I need…