Likely a Port is your best option, it offers line-in and line-out to connect to other systems.

A used Connect would work too, make sure it is S2 compatible.

Thanks! I understand I need to connect speakers to the line-out. Am not sure though I can identify the line-out of the tuner (image attached). Will the DCC REC out work for this?

I would try to connect that DCC Rec (out)  for the line in to the Port, and the Play (in) to the Port’s line out. which should be the line level output that Sonos is looking for. Not quite sure what DCC is, on this device, I’m assuming that is some sort of tape loop. 

You do not want to connect speakers to the line-out that is only for interconnecting audio devices like your Panasonic and the Sonos Port.

The Sonos Port is not a speaker, but a device that is connected to your stereo as described above. It will bring Sonos sources (like Spotify) into your stereo and the sound from the stereo into the Sonos system, where you can play them to other Sonos speakers via the “group” function.

Thanks a lot for your advices!