In HDCP Mode: No NAT within LAN
Sorry, no english.
In DHCP mode, connected with an internet router, disable NAT for communications within LAN.
The internet router knows all local networks and so should know also amplifi.
For example: On my internet router I add the network of the amplifi
192.168.192.0/24 gateway 192.168.100.130 (the ip address of the amplifi on the internet router). on the amplifi I will add the routes for all other LANs 192.168.100.0/24 gateway 192.168.100.1, 192.168.101.0/24 gateway 192.168.100.1 and so on.