It’s quite likely the connected TV does not support the pass-through of the DTS codec through its ports and so the audio reverts back to PCM stereo

I’m using a Sony A80J. Apparently it does support DTS?

Yes indeed, I just checked and that is the case - so perhaps check the source Player and/or the App you are using and see what the audio-output settings are. If the issues persist, try powering off all devices (not standby) for a few minutes and see if that perhaps resolves the issue.

Is your Beam still running S1? DTS is S2 only, and it also requires a TV that passes it through (and according to rtings it does).

Try this:

On the supplied remote, press the HOME button, select  Settings, and then change the following settings on your TV:

• Under TV category, select Sound.
  • Select Speakers > Audio system.
  • Select Digital audio out > Auto 1 or Auto 2.
  • Select System sounds > Set to off.
• Under System Preferences category, select Accessibility.
  • Select TalkBack > Off.
  • Select Screen reader > Off.

I love Sonos! really now with its dts support, finally with all or at least most of my blu-rays I now have the full 5.1 surround experience!