Originally Posted by Doctego
If the sources are connected to the AVR/soundbar via HDMI and then the AVR/soundbar is connected to the TV via HDMI, there is no need for the optical connection from the TV to the soundbar. This is the ideal method of connection. The only reason why you might also need an optical cable is if you have more sources than your AVR/soundbar has HDMI inputs.
Thank you for responding Doctego
This soundbar, the Vizio S4251W-B4 does not have HDMI
The only inputs are: Digital Optical Cable, Digital Coaxial Cable, 3.5MM, RCA
So it seems, the best audio quality would come from AVR out via optical to the soundbar (since optical out from TV would be downmixed into PCM - digital stereo).
I believe that might be the best audio, but it would be great if someone can confirm this. Having real-world experience and advice is always helpful. Also hoping anyone can advise if there are any difficulties or surprises with this setup with using this soundbar.