I live in a '70 two story house.  The internet comes in from the upper level and it's difficult for the wi-fi signal to reach lower level.  In my current setup, the main internet goes through an ASUS router/access point, which is then wired through a TL-WPA8630 powerline adapter to reach lower level.  Both the ASUS router and the TL-WPA8630 adapter downstairs are configured using same SSID.

I am thinking of purchasing a Deco M9 Plus from Costco, set it up as the main router, and wire it to my existing WPA8630 adapters.  For the downstairs WPA8630 adapter, I would turn off its wi-fi signal, and connect it to a 2nd M9 node.  My question is, how would the primary M9 node upstairs talk to the secondary M9 node downstairs?  Would it go through the powerline adapter, or through its backhaul wireless signal?  Would I be able to take advantage of my existing WPA8630 adapters, or do I have to buy a Deco P7 or P9 bundle for the powerline solution to work?