Ok thanks for helping 

Do you have any other solution like for example a receiver or dongle or anything else 

If you want to use something other than the Apple TV for Atmos, as you only have HDMI-ARC, you’ll need a player/dongle that uses Dolby Digital Plus for its Dolby Atmos, according to this article.

https://support.sonos.com/en-gb/article/listen-to-dolby-atmos-on-sonos

I think the latest Fire Sticks use Dolby TrueHD for its Atmos, so that isn’t going to work either. Not sure about the Roku stick.

But you said Chromecast and your TV’s built-in apps give you Atmos - so why not just use those? Unless I am misunderstanding your question. 

Yup that’s right I can use the built in apps or chrome cast  but I prefer using apple tv because of Apple ecosystem 

I know what you mean. I wouldn’t want to not be using my Apple TV for overall experience. At some point you’d need to get a new TV unfortunately to get Dolby Atmos from it on your Arc…