Not sure what you’re looking for, but there’s a pretty extensive thread in Announcements that covers all of your questions. 

To boil it down, your current speakers will work with the Arc when it comes out next week, but the software that supports it hasn’t yet been released, so we’re not sure if there’s a special update process, or you simply unbond the Sub and surrounds from the current device, add the new device, and then re bond the Sub and surrounds 

Your issue, as has been discussed at length in that thread, will be getting an HDMI ARC or eARC signal to the Sonos Arc. 

My query isn’t  about speaker compatibility - I want to make sure I am able to get Atmos surround sound from Xbox one X apps like Netflix, Prime and the 4k drive into Arc. I do not have a TV and there were threads that spoke about Apple 4K TV being incompatible when connected to Sonos directly. In my case and my current setup -

Xbox One X is connected to Sonos via optical cable. 
for the new setup, Xbox one X will to be connected to Arc via HDMI.

What device is creating the HDMI ARC signal?

Sonos reads HDMI ARC, or eARC, but does not read an HDMI input. And none of your source devices generate an ARC signal. That’s most frequently reserved for a Television. All of this is covered, as I said, in the thread I linked to. 

I have same doubts of Kenzi but everyone reply it’s not possible.

still I cannot understand why Arc should not be able to read hdmi signal and he can read an HDMI-arc one.

the returning part of the signal is obviously useless in this case but why Sonos should refuse to read the audio part of the HDMI signal?