I don't think you can do that. To replace Maxis home fibre router, you need a router that supports VLAN tagging.

From what I find on the web, Xiaomi Router 3 dont have VLAN tagging in its specification. (I might be wrong)

I got my router replaced with a Asus RT-AC66U. Asus has build in firmware that support Maxis Fibre. All I need to do is to select Maxis Fibre and it configure itself.

Connect ur XM router to Maxis Thomson router. Disable Thomson router's wifi.

Bump, i wanna know how it ended.
I plan to swab away the thompson router too, but i need the voip phone service.
My current setup is, the fibre enters my house and connects to a modem™ and the modem connects to thompson router with the wifi disabled but voip still working.
And lastly, the thompson connects to an asus router (rt-14uhp) for wifi.

everything works fine, exept that asus router did not meet my expectation, coverage is not as good, maybe ac will solve my coverage problem.