You could, but (a) you’d only have Dolby 5.1, not DD+ or Atmos, but much worse (b) the soundbars would probably be slightly out of sync with one another, owing to having different audio processing pipelines

Thanks I appreciate the reply.
Meant to add initially that I could set the Playbar up, as an individual speaker, and group it as a ‘helping hand’ for the fuller sound. Wouldn’t that acted I the truck as well?

i was nit aware that I would lose the DD+ capability by spitting the signal. I appreciate that being pointed out.

 Thanks very much.

You can’t send DD+ over optical.

As for grouping the Playbar, it would be behind the Arc for TV audio (but in sync for music) the same as with any grouped speaker. There would be a horrid echo.

What if an HDMI splitter or if Playbar is setup as stand-alone speaker then ‘grouped’ in app.

 Thanks for your help? 

If you group the Playbar via the Sonos App, the delay is still the same, you will encounter an echo for TV audio.

But with music audio it will sync, if adjusted via app?

 Thanks for your input.

Is that true even with HDMI splitter as opposed to optical?

 Thanks 

Yes, music audio will play fine (in sync) when your speakers are ‘grouped’. The HDMI/Optical input is irrelevant, as that is for TV audio.