Replace NOS router

Bom dia, sorry to write in english but my Portuguese is still too limited. I wish to replace my NOS power router with my own Asus router and wonder if that is possible? The reason is that I have a smart home setup from IKEA (trådfri) and a speakersystem SONOS and the don't work well with the NOS router. I have been in contact with both IKEA support and SONOS support and we can't make it work well. My guess is that the DNS service in the NOS router is not working well. I have tried to set the NOS router to use fixed ip-adresses but then everything stoped working. I tried to connect my Asus router directly to the fiber modem but the router did not connect to the WAN. What I have done now is to use the Asus router as an access point for Wifi after the NOS router. The Sonos system works now better but still the IKEA system does not. The problem with the IKEA system is that the IKEA gateway, connected to directly to the NOS-router via ethernet constantly disconnect from the LAN.