Your sonos has its own mesh network independent of wifi i think.
Nono. Those routers that you buy off the shelf like ASUS AC68, Netgear Nighthawk etc aren't primarily designed to work like this and dont provide the same advantages as professional, enterprise-grade stuff does.
You can ask Repsol why his AC88 has been relegated to simple routing duties while the actual broadcasting is done by his professional access points like the one below.
https://www.ubnt.com/unifi/unifi-ap-ac-pro/
Also a big problem is that consumer-grade products dont use Power over Ethernet. You have to run your network cabling in addition to your power brick. Whereas for my setups, i centralise everything i need in the DB box and all I have to do is run a single ethernet cable to each Access Point and its all done. The access points can be 30 or 50m away it doesnt matter.
Whereas if you use your AC68, it's likely that you'll hide it in your network closet near to your door or your tv console at the front of your house. That is horrible placement and worsens the range because you're essentially broadcasting to your neighbour.