I am using the Playbar, Sub and 2 Play 1s as my 5.1 home theatre solution.
After some research, it seems clear SONOS made a terrible choice in having optical cable (TOSLINK) being their only link to the TV. When I have a lossless audio format in my media, like DTS-HD or Dolby TrueHD, or 5.1 channel PCM, the optical cable does not have the bandwidth to play that audio format correctly. I get a downmix or else an "unsupported audio" error message.
If you force your TV to use PCM, you are forcing a downmix to 2 channel audio. A new TV may do a "simulated" 5.1 channels, but it will never be true surround sound.
Is there any way to get DTS-HD, Dolby TrueHD or Dolby ATMOS working on SONOS?