Not 100% sure I comprehend your post. You should be able to replace your AVR with an Arc, which incorporates left, center, right, an upward firing Atmos speakers, along with a Sub, and a pair of Sonos One SLs. 

However, I’m confused about two things. One is your use of the term ‘center’, and second, what purpose you’re proposing for the Amp. Is your intent to use the Amp to drive front right and left speakers, and use the Arc as merely a center channel? If so, I would suspect you’ve figured out that there is currently no configuration in Sonos that supports a separate center speaker, along with separate  right and left fronts. All of Sonos’ sound bars already contain the left, center and right signal, even the Amp creates a ‘faux’ center channel, but doesn’t allow a distinct center channel speaker.

This type of setup has frequently been requested over the years, with distinct speakers for front left, center and right channels, but so far, Sonos has not released any support for this type of system.

Hi Bruce,

yes you got it right.

In this specific case the intention would be to use ARC only as a central front channel. This need arises for two reasons:

1) The two front right and left PROAC 3.5 speakers are absolute references and I use them mainly for listening to jazz and rock. It would therefore be a great pity not to be able to use them also in the home theater configuration.

2) The TV and ARC bar are recessed slightly so the sound from the left and right channels of the ARC is focused correctly.

Thank you.

No soundbar in existence lets you use it as a center channel.  The very definition of a soundbar is the Left-Center-Right channels located in the same enclosure.  

I agree with @jgatie .  It’s a soundbar based system.  If it is vital to you to keep using your speakers then you need another product.  A Sonos Amp could be used for front speakers, and it then creates a ‘phantom’ centre channel, as mentioned by Bruce.  

Interesting, so i should give up ARC and compose home theater system with AMP for the two front, SUB 3th generation and pair of ONE as surround.

So can you confirm that these products can coexist within the same ecosystem?

But, tell me more about the "phantom" center channel that would be created by AMP...

Yes, all of those products would work together in one ecosystem.

Not sure what you want in terms of extra information that hasn’t already been said in many places on the internet, including Sonos’ website, and these forums. The Amp uses the two front speakers to create a faux center channel. I don’t recall ever seeing anyone posting about issues with that setup, although I don’t have it myself, so my information is second hand. 

Although not germane to your particular situation, for others who may come across this thread, the Subwoofer output on a Sonos Amp is not available when it’s being used to power surround speakers. Since you’re using it as powering your front speakers, it would indeed bond as desired. 

The subwoofer thing would only be an issue for a non-Sonos subwoofer. Looks like @McCallister is considering a Sonos Sub, so that would be fine anyway.

The 'phantom' centre is achieved by splitting the centre channel equally between left and right front, so it sounds like it is coming from the centre. 

Very good,

I already have all the products, I just have to start testing.

Too bad having to give up ARC since I already bought it.

At this point I would also ask you another question: Can products like ARC or AMP be shared across ecosystems?

I'll explain. On the TV I have several HDMI-eARC ports; could I create an ecosystem with ARC and SUB 3th gen, and another with AMP and the same SUB, both connected to the TV or other devices (game consoles, satellite decoders, etc.)?

Let me restate that, as I think your use of “ecosystem” isn’t what I understand as “ecosystem”.

To me, an ecosystem is equivalent to a Sonos House Hold, up to 32 speakers in any combination, assigned to a variety of “rooms” as specified in the Sonos software, although physically placed anywhere, within a network served by the same LAN subnet.

I think you’re trying to use the word “ecosystem” to mean a “room” in the Sonos software, i.e. a defined group of Sonos devices dedicated to work together, and also with other “rooms” in the Sonos house hold. 

As stated, you can have up to 32 Sonos devices in your “system/ecosystem/ house hold / setup. They will be defined in groups by room “names”.

What I think you’re driving at here is “can I share the same Sub in two different “room” contexts at the same time. The answer to that, sadly, is no. Any Sonos device is dedicated to a single “room”, and can’t be shared by different “rooms”. You can easily “group” rooms together, so they’ll play the same streaming music in sync, but that becomes more complex because the concept of a Sonos Home Theater “room” is a subset of the normal Sonos system. 

If you were to “share” the Sub between two rooms, you’d need to “un-bond” it from the Amp/Arc each time, and then bond it to the other. Which would, if you choose to use TruePlay, would erase that for each room when you “moved” the subwoofer. 

If I’m misunderstanding your statement, please let me know. I want to give you a direct answer that we both understand :)

If the L/R 3rd party speakers image well and are relatively close to the TV screen, the center channel speaker is redundant. If the L/R speakers are widely placed or image poorly, you’ll start to notice a “hole in the center” without an actual center speaker.

Part of the attraction of soundbars is quick and easy setup with low room clutter. The results can be very satisfying. A full surround system with multiple speakers (properly placed) can be a more immersive experience. That said, there are some interesting demos circulating at trade shows and in academic settings that give very good surround with only two speakers. This technology is not and may not ever be ready for full deployment.

Hi Bruce,

I probably didn't express myself correctly but you understood exactly what I meant. I figured "sharing" wasn't feasible but it might be desirable.
Just as it would be desirable for Sonos engineers to give the possibility of making ARC a pure central channel in an "advanced home theater" setup.
Thank you all

The current LR front loudspeakers are the absolute reference in the reconstruction of the soundstage.

I hope they can do an equally great job in rebuilding of the ghost channel.

This weekend I just have to put ARC aside and try with AMP this new 2.0.2.1 configuration ...

Please post back with how it goes.

Absolutely

Here I am, today I did a lot of tests.
What I can say is that if you have a pair of reference speakers, the choice to drive them with AMP is a winner.

I have not encountered any low volume issues in speech. I've read several conflicting opinions about the "phantom center channel" but in my case everything works for the best.

It being understood that ARC is an excellent all-in-one product, however in my case it is absolutely not comparable to the acoustic performance of AMP + ProAc 3.5.
Thanks for your suggestions.