Hi @kevinheather . With FTTN, you need the RJ11 connection from the TP-Link router (VR1600 is it?) to the telephone wall socket. The RAX10 has no RJ11, only RJ45 for connection to an NBN box. The RAX10 can be used as an extender to the TP-Link, or TP-Link can be put into bridge mode and RAX10 manages the home network.
@kevinheather . A few points:
You can check the DSL info in the VR1600 for the down and up speeds the router is getting, and line characteristics.
What speed plan are you on? What speeds do you get using the speed test on TPG's support page?
Does the buffering occur at particular times (evening?)?
This iiNet article has a selection of routers for FTTN and shows how to set VLAN ID.