The Arc cannot be used just as a center speaker. It’s role is to do all the HT surround channels including two upward firing reflective channels for Atmos audio and the front audio channels cannot be sent/diverted to any other speakers. Only the two rear channels and the .LFE channel can be passed onto other Sonos devices.
 

A Sonos Amp can be used either for the front left/right channels which involves a phantom center channel, or an Amp can be used separately for the two rear surround channels. Note: when the Amp is used for the rear channels, the available ports on the rear of the Amp are disabled. Each of the Amp roles mentioned, can be played to either one, two, or in some cases three ‘pairs’ of speakers, but whatever paired speakers are attached, they will all play either to the two front, or the two rear channels.
 

So, just as a quick example, you could have one Sonos amp with say two ‘pairs’ of speakers  playing the front audio channels and the .LFE channel …and another separate Sonos Amp with two ‘pairs’ of speakers playing the two rear surround channels.

Ken_Griffiths…..firstly thank you for your reply and writing to me , what I understood from your explanation is we can't us the 3rd party Denon AVR right ? And we can use Sonos Amp for 1 pair of. in celling speaker and for the rear in celling speaker I can use the other Sonos amp right ? 

I understand that we can not use the Arc as centre speaker. 

So is it possible to make 5.2.2 right ??   

Assuming you are looking for Atmos audio output, as one further example, you could use the Sonos Arc for the front Left/Center/Right/Upward-firing audio channels and a separate Sonos Amp for the two rear channels, perhaps using a ceiling speaker pair, that’s if the ceiling speakers are set at an appropriate place in the room.. (I’m personally not a fan of HT front or rear-channel surround audio involving ceiling speakers). I personally prefer those channels to be set at shoulder/head height, when seated, but that’s a matter for your own consideration.

An alternative would be to perhaps use two Sonos One SL’s for the rear surrounds and then utilise a separate Sonos Amp for the 4 ceiling speakers for music audio only, which can of course be ‘grouped’ with the Sonos HT setup for music Playback, but that might likely be overkill for the room, but it maybe worth thinking about, if the ceiling speakers are already in situ and not ideally placed for TV surround audio.

With any Sonos HT setup, you can utilise either one, or two, Sonos Subs as part of the setup, as long as one of the Subs is a gen3 model.

Hope that info. assists.