ok, we're getting somewhere now - sorry I was stuck in traffic after being on-site with a client.
I would check to ensure the firewall also has ports for:
NETBIOS naming
1434 for SQL Browsing Service
135 for T-SQL Debugging (for future use)
I believe the issue will be with the 1434 port, as it states it can't see the server after it is enabled with 1433 open. Please open those ports and let me know if that doesn't fix it
*crosses fingers*