You are supposed to either have a VPN setup or a Coral Sentinel. That being the case I have had it working in situations you described. You have to remember that the public IP of the remote station has to be unique to all connected. You never forward anything to the media gateway card. It's always to the UGW and its UDP. Easiest way to see if your firewall is hosing it up, is putting the UGW in front of it (prob need another pub IP to test it this way). I would have no problems exposing the UGW as it's not a windows device and can't be hacked. Trust me it's gonna be your firwall screwing things up if nothing is being blocked by your provider. Just check your IP setting on the UGW card to make sure it's looking back at the gateway (router).
Also:
Make sure that the firewall sends ports 16400 thru 16992 (UDP) to the gateway.
