no dts on Playbar

The playbar will only play the audio sent to it by the connected device. You will need to check the player or any devices that the audio passes through, like a TV for example, to see if it can ‘pass-through’ the DTS format, if not, the device concerned might be transcoding the audio to PCM stereo

Even fairly recent Panasonic TVs won't pass surround sound formats from HDMI sources.

I am using an optical connection 

You likely need to check the pass-through abilities of the connected device.

When you say you are using the latest Sonos app do you mean the latest version for either S1 or S2 or are you using S2 exclusively?

Also if the source is a DVD player it may be transcoding DTS to Digital 5.0 or PCM.

I am using s2 version 13.4.1

What is the specific source? What title? Is it on Blu-ray? DVD? What specific model Blu-ray or DVD player are you using? What specific model TV do you have? We need more info to assist you further.

I am playing a mkv file with dts sound

and am playing it through Nvidia shield

In the advanced sound-out settings on the Shield set the codec manually to use the DTS only codec.. check the connected TV allows DTS pass-through.. if the latter doesn’t, you will only get PCM stereo no matter what… the only way around it would be to use an audio extractor/splitter to bypass the TV ports.

ok will give it a go

thanks