Bass unit - generation 2

Cellular modem? 

On this list?

https://support.sonos.com/en-us/article/incompatible-network-hardware

Unsuppported list:

https://support.sonos.com/en-us/article/sonos-system-requirements

Bass unit (I assume you mean a Sub?) is designed to ‘bond’ with another, appropriate Sonos speaker. It isn’t a separate device that shows up as a ‘room’ in Sonos software, so what device are you attempting to add it to? Is the ‘WiFi/radio’ turned on on that device, so it can communicate with the Sub?

Have you rebooted/ power cycled all the devices, including the router? Did you call Sonos Support to discuss it? What did they say?

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Would it be possible to set up your new router with the same SSID and password as the old router had?