I am revisiting this old thread https://www.geekzone.co.nz/forums.asp?forumid=85&topicid=239726 in the hopes that we can make some further progress with:
a) Updating the beta - https://en.avm.de/fritz-lab/fritz-lab-for-fritzbox-7490-and-7590/overview/ and yes I did try this a couple of times
b) Be able to successfully port forward to another router that is hanging off the Fritzbox. I have DMZ'd the Fritzbox and setup the DDNS host so it should pass through the port forwarding rule. It passes the LAN address fine, so I just want to make sure I am doing this part right.
Thanks for your attention.