Thank you very much for your answer, it helped me a lot!

The part converts digital SPDIF signals into analogue ones. If your TV has a digital coax or optical Toslink output and the Sonos has an analogue input, it works. The other way round does not work. The Sonos only seems to have a Toslink input. So unfortunately it doesn't seem to work. It is unusual for TVs not to have an optical output.