The TP-Link "RE900XD Wi-Fi 6 WLAN Repeater AX6000" can be used with the Sunrise internet box, but there are a few things to bear in mind:

- WiFi repeaters like the RE900XD are generally compatible with most routers and internet boxes, including Sunrise's, as they work by amplifying the existing WiFi signal.
- However, for optimum integration, we recommend checking that the repeater is correctly configured to connect to the Sunrise box's WiFi network. Sunrise Smart WiFi Extenders are specifically designed to work with modems from the Connect Box family, but third-party repeaters such as the RE900XD can still work well if configured correctly.

In summary, the RE900XD should be compatible with the Sunrise internet box, but proper configuration is required to ensure a stable and optimal connection.