Are you asking if such a cable exists, or saying you have one that doesn’t work? 
 

Since the Five buffers sound before playing, you may find lip-sync is an issue if you do use the Five for this application. This buffer in inherent in Sonos devices to enable sync’d multi-room setups, even if only one speaker is in use. 

I have the cable and it isn’t working. I am trying to figure out how to successfully connect my LG TV to my Sonos 5. Any recommendations? 

The Sonos Five has an analog line in (3.5mm). Does your TV have an analog line out at all, or are you restricted to this optical digital output? 

One of the issues, in addition to the delay @nik9669a mentions, is that the Sonos, not being designed for television use, will only interpret a stereo signal. Which means if you are using an optical cable adapter, you’ll need to somehow restrict the output on your TV from the normal multichannel digital optical output to only a stereo signal, so the adapter can process it and send it on to the Sonos Five.

Do you have a link that you could share with us as to the cable you’re using? We might be able to give you more helpful suggestions if we were aware of specifics, such as which cable you’re using, and which LG TV you have. 

Aloha Bruce!

My TV has optical and HDMI, no analog connection is available. I really appreciate the information. After I move in a few months I will look at setting up a whole system - I really love sound. I will need to do some research to learn a bit more so I understand how everything works together. Mahalo for your reply, it is very helpful and informative