Facebook to me anyway seems less substantial and irreverent compared to the main forum which is more formalised and structured. Facebook isn’t structured in that way it provides headline articles in the same way that 24 hour news does with a limited look back facility.
The HMVF Facebook site should be different to cater for the people who will not join a structured forum but who would be willing to join a Facebook page where they can jot a few lines down and add a like or two and move on to the next story.
My gut feeling is that you should link threads from the forum as it does now and share them into the different groups that exist in Facebook land, in that way more people will be willing to look at and maybe join the forum when they see the articles / threads.