Yes, the Xiaomi AX3000, as well as other mesh routers, can be used with any existing router from an internet provider.

The idea of a mesh router is to create a WiFi network that allows uninterrupted WiFi throughout the house or flat. Devices can be moved from one place to another within the area covered by the mesh WiFi without interruption and always connect automatically to the next stronger transmitting mesh router.

The set consists of two identical mesh routers. The first of these is then connected to the LAN cable and placed near the Internet provider's router. Its WLAN is switched off, as it is not really good anyway. The mesh routers then take over the entire WLAN traffic.

The Xiaomi AX3000 system can also be expanded if necessary, up to 256 devices can be used in the mesh.m

It is best to connect to the Sunrise VDSL with an Ethernet cable and thus set up a mesh network.