Hi, I have recently purchased a Sony UBP-X700 and a Sony Bravia KD49XF9005 UHD TV. I also have a Sonos setup (Playbar, Sub and 2xPlay 1s) used mainly for music but occasionally used for home cinema surround sound. While excellent for music the Sonos system could politely be called "primitive" when it comes to home cinema. 

The Playbar has a single optical connection and will support only stereo or 5.1. With my TV/BluRay player, the simplest connection is the optical output from the TV. I can also connect using a co-ax/optical converter from the UBP-X700 bluray player. Both work fine when I have a disk with a 5.1 audio track but with more recent disks there is only a 7.1 audio track. With these disks, I've only been able to get stereo sound on the Sonos.

I've been playing around with the audio settings on the TV and the player. The player has a promising looking option called "Downmix" with a setting of either "Stereo" or "Surround". On "Stereo" setting, I get the expected stereo on the Sonos. On the "Surround" setting, I get silence with the Sonos reporting an "unsupported audio format". Does anyone know what Downmix is doing to the 7.1 track and what audio format it is downmixing to? 

Any ideas on how to get to a simple(!) 5.1 format or am I stuck with stereo.