Double check if your Giga hub has a dedicated 10G port like my unit does. If so then use that port and double check the link speed for your WAN port on the Asus unit.
I can imagine exactly what kind of person(s) is directly responsible for causing and not fixing this kind of problem but I found a TP-Link fourm post about setting the MAC address of the 3rd party router/firewalls wan port under DMZ (Advanced DMZ) an...
What has been done on this front. As of may 5th (I have Logs!!) my internet from 3rd party hardware has been capped at 300/300. This is a known issue they you are exploiting and or using deliberately to handicap Paying clients internet service!