Is the Cambridge CNX v2 a streamer? It is unlikely to be a direct connection to a Sonos Beam. The Beam is expecting an ARC input, not a standard HDMI audio input, although Sonos does have an optical adapter, so if your Cambridge device has an optical output, that could work. But Sonos’ own software is a capable streamer in its own right, not sure why you would want to connect a third party streaming device to a Sonos. 

Thanks for the reply. 

In fact now it works with the adapter, I had already tried without success, after your suggestion I tried again by removing the analogue connection to the amplifier.Thank you.