I’m struggling with this too. Mine is LG C8 with Apple tv4k and PS4. 
Apple tv works fine.

i tried PS4 using GoT blu Ray which has Atmos soundtrack, if I put in bit stream output setting (Dolby or DTS) I get lip sync issues and app shows 5.1 as the output. No settings achieve Atmos.

For the C9 make sure the TV firmware is current. Also keep an eye out in the next few months for more firmware updates for the C9. There is an extensive post of C9-success elsewhere today.

Can’t speak to C8 issues, except fixing any is likely a lower priority for LG than C9.

Turns out I don’t use the BD feature on the PS4 enough to know there’s an additional audio setting once you are playing the content. So obviously you will need to check in the global system audio settings to make sure you have output set to ARC with Bitstream (Dolby). Once you confirm that, start the disc with the Atmos track and as soon as the video is playing, press square on the DS4 and check that you have this option set: 

Select "Settings" > "Audio Format" > "Bitstream (Direct)".

My PS4 was set to LPCM for some reason so that’s why I was getting 2.0 stereo. Detailed instructions here: https://denon.custhelp.com/app/answers/detail/a_id/5868/~/setting-your-sony-playstation-4-to-output-bitstream-audio-%28dolby-digital-%2F-dts%29

I hope this fixes it for you as well. Cheers!

Thanks that works to get Dolby atmos through but then frustratingly get the lip sync issue 

Are you using “ethernet” HDMI cables?