Hi - I have same setup and same problem setting up remote access on a BT Business Hub BT 2700HGV, though it worked perfectly on my previous BT Home Hub 2.
I set up port forwarding manually but without success and then tried your suggestion of putting the server in DMZ (temporarily to test), but I still cant remote access the server on either IP or homeserver subdomain - 'server not found'
I do get a ping response from the myserrvername.homeserver.com.
You mentioned setting up a static IP, is this necessary?
Is there an online guide for setting up a windows server on a BT 2700HGV anywhere?
Thanks