Can you post your make/model of the ‘stereo’ that you wish to connect and what are the Sonos players you are looking to connect it to, or are you just looking to play the services available via the Sonos App/Airplay to your stereo?

In general, without the specifics that @Ken_Griffiths is asking for, you should be looking at a Sonos Port, which can be attached to a standard amplifier’s tape loop, and provide a Sonos stream to the wired speakers. 

A Port. And no bridge (or Boost, its modern equivalent) is required. Simply put the Port on the router’s WiFi, ideally the 5GHz band (signal range permitting),

I’d assumed the word ‘bridge’ was in its standard context as a thing between two systems, and not actually the Sonos product no longer made. Perhaps erroneous of me.