One issue you may be running into is if you are trying to set up the dyndns.tv on your dns. I think it would have to be set up on their dns servers pointing the subdomain to your server and also to your name servers. Then your other sites could be handled by your local name server.
I have 5 sites up and running under ISPConfig3. One of them is thru the DNS servers at dyndns.com but not using their domain name. And I only do that for the dynamic IP update my router will automatically do if my IP changes. I may dump them if my own updating scheme works ok.