Cut out the middle man, buy a decent new router.
The Asus is a decent router
Have you ever owned the DSL-AC68U?
It really isn't a decent device.
I have owned both the RT-AC68U and the DSL-AC68U.
The RT-AC68U is excellent and I still use it to this day.
I wouldn't recommend the DSL-AC68U as a doorstop for fear that it will break your door.
The Asus DSL modems with Mediatek chipsets are the only chipset I'm aware of that allow disabling of UPBO (a shocking setting to allow an end user to disable) and the only chipset I'm aware of that OpenReach have actively banned from using G.INP.
There was a specific modem that when in use on a DSLAM broke the DLM for every other line on the DSLAM.
OpenReach never confirmed what the device was but many of us suspect it to be these Asus modems.
OpenReach have since amended the DLM to work around the issue the modem in question was causing.
The Asus RT devices firmwares are maintained by a different department to that of their DSL devices.
I praise their RT models and recommend them frequently.
I do the opposite with the DSL models.