I'll have to give a plug for my company Indaba Music here - http://indabamusic.com http://indabamusic.com Our site was pretty much designed exactly for this us

I'll have to give a plug for my company Indaba Music here - http://indabamusic.com http://indabamusic.com Our site was pretty much designed exactly for this use case - the free account allows for private sessions, in-song commenting and in-session discussion.