In reply to a post by prlzx:

Discovery methods vary but increasingly use multicast rather than broadcast
- mDNS (Avahi/Bonjour), uPNP, WS-Discovery and SSDP are not uncommon.

Spot on.

I've an old hub (hub not switch) and WAP and connected via that and confirmed that the app can find the Humax box. I was then able to connect a laptop to the hub and use wireshark to find out what happens when a successful connection is made. I'm seeing packets going out to 224.0.0.22 (IGMPv3) and 239.255.255.250 (SSDP).

Is the Fritz blocking port 1900 in the firewall settings?