Two Arc's in one room.

No. Each Arc is its own individual zone. You can “group” two zones together, but grouping two Arcs together to play audio is not a good idea. There are much better ways to fill your room with sound.

What are the dimensions of the room?  most likely it will make more sense to use an amp to run front speakers an an amp for the rear.  If not that, then go with an non-Sonos setup with a Port if you want to connect it to Sonos.

thank you for your replies, 

Room is 26ft x 42ft with a 25ft vaulted ceiling. the design of the room allows me to add arcs that hidden.

the current audio installation is 4 sonance plaster in speakers driven by a large amplifier linked to a sonos connect.

the aesthetics of the room unfortunately does not allow me to install any other products easily and this the reason I am looking to try use two Arc’s

@MarkG7 Are you only playing music in the room?

@GuitarSuperstar

Yes only using the room for music, I have the perfect slot in the beams running across the room to place an Arc

That’s a beautiful space.

If you are only using the room for music, I think the two Arcs will work. And you could connect a Sub to one of the Arcs and group your Connect and two Arcs together to play music. If you move forward with the setup, please report back how it sounds in that room. I am curious to know.

thank you for your replies, I am going to give this a try and will let you know how it works out.

To be clear, you could use 2 Arcs for music only as you’re thinking, but they would not be one zone, but two.  As well, you could trueplay each Arc separately, but you could not tune them as a single room. I don’t know that I would trueplay anyway, since the Arcs are not designed to be place up high in beams like that.

Why are you unsatisfied with the 4 ceiling speakers you currently have?  If they don’t get loud enough, have you considered using a different amp (or two amps)?    Although they might not look as good, 5s would be a better choice for this room.

Each Arc would be a stereo pair of speakers in this situation. So not a lot of stereo separation in this space you have. I share melvimbe’s thoughts here, I’d be much more tempted to use the Sonos Five (four of them), which you could separate much more widely. Or even some Sonance in-wall/ceiling speakers driven by a pair of Sonos Amps. 

I would agree as above using 2 amps with the existing speakers. The Arcs are optimized for a home theater environment. You could even add 2/4 Fives withe the existing 4 as well.