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.