Hmm... Filebrowser and VLC? I know you are using AFP, but can you make that folder also SMB? I know this works because this is what I use to access folders on my 4 disk storage center.
I do not do AVI though, so I am guessing at this point re: vlc working for avi's. I think it does.
Also have you tried
streamtome? It isn't free and you need a server per say running? I don't know if your nas can run any server type software or not.