This must be an issues with settings
AFAIK, the Sonos Playbar *is* designed to handle & stream output from an audio source via digital optical input. So IOW, it could be an HDTV or other component which could output sound via digital optical. My bet's on the settings somewhere in the chain that are incorrect. The Sonos connect would be the 'last mile' you would indeed utilize, to connect via digital optical or digital coaxial cable to your AV receiver.
Luckily, the Sonos forums (as well as AVS) are helpful in solving what their techs often cannot.
That said, I can't even begin to tell you how much better even an entry level HTIB (home theater in a box) would be sound-quality wise above overpriced soundbar solutions such as this one. Not only would this get you great bass, but proper dynamic range/soundfield/ability to dock an iPod/etc. You also won't be getting surround sound from the Playbar. Add up the cost of all that Sonos gear and you could substitute with some better sounding gear IMNSHO. Bob's advice to stick with a simple wired connection from Samsung to AV receiver would be my choice too, given you will have three 'hops' before it's sent to the receiver. There are plenty of good ways to hide a longer wire too, just ask at AVS when you visit that forum. Youtube also has some great DIY wiring videos.
Adding an AppleTV or Apple Airport Express has proven to be a great alternative to adding audio streaming to a home AV setup over wifi. Using the Apple Airplay built into iPod/iPhone/iPad, you can stream to the AppleTV or Airport Express, and that routes via digital optical to a nearby receiver.
I assume you have no cable or satellite box in this mix?