You can only add two surround speakers to a Sonos home theater setup. So you would have to choose between adding two in-wall or two in-ceiling speakers to use as surrounds. You cannot use both with the Arc.

Even though the Era 300s are the best option for surrounds, if you are seated within 7-10 feet from the Arc and have standard 8-9 foot flat ceilings, the Arc will provide sufficient height channel effects so the Era 300s aren’t completely necessary.

Thanks for the info @GuitarSuperstar.

The sofa is about 15ft from the TV and Arc and has 9 foot to the ceiling. 

Would in ceiling or in wall speakers be preferable?

Or,  since I am quite far from the Tv maybe the Era 300s would be best?

Unfortunately, from 15 feet away, you won’t hear much height channel effects from the Arc. So the Era 300s would definitely be the best option if you really want to hear any sound effects above you when playing Dolby Atmos audio.

Choosing between in-wall or in-ceiling for surrounds is a toss up. In-wall surrounds are good because you can install the speakers at ear level which is ideal. But some people (possibly your wife) may not like the aesthetics of having speaker grills on their walls. In-ceiling surrounds are the least noticeable and probably your wife’s preference out of the three options. And because they are in the ceiling, they could make it feel like the surround audio is coming from above you similar to Atmos height effects. But, at the same time, surround effects that should sound like they are behind you are coming from above you, if that makes sense.

It does,  thanks very much for your insight.  Appreciated!

Helpful comments.  Thanks.  I have a similar set up Mhenegan--arc soundbar (with sub) connected to a big tv with 9 ft ceilings and 15 ft viewing distance.  I'm thinking of adding ceiling speakers to function as rear surrounds.  But I can only place them directly overhead if the viewing seats rather than a few feet behind (and overhead).  Will that set up provide surround sound?  Is it better than sticking with the arc-sub-TV setup?   

I assume you can’t place surround speakers in a better position behind the seating area?  That’s obviously what you should do if you can.

To your direct question, it’s a matter of personal opinion, but I would not place surround speakers in the ceiling like this.  You’ll hear audio from them, and it will be interesting, but it’s far from the intended design for an atmos setup.  I think I would just go without surround, and let the Arc bounce audio off the walls and ceiling till I can find a better solution.

Hi @Randy Rattlesnake 

@melvimbe is correct it’s a matter of personal preference but not ideal. 

Question:

Is the seating up against a wall or some type of stadium Home Theater (HT) seating?

If allowed you could place Era 100’s or Era 300’s on stands to the left and right even if the seating is up against a wall. However in doing so the surround sound will be more prominent to whomever is seated closest to a surround speaker in some situations.

The Era 300’s will compete the Dolby Atmos experience.

Thanks for the response.  The seating is a couch against the wall (not stadium seating).  The wall is mostly glass, as well.  Era300’s is a great suggestion, especially since that jumps me up to an atmos system.  But I don't think I can get those prominent speakers past the decorating committee.  
 

In sum, it sounds like you think less than ideally positioned ceiling speakers for rear channel surrounds is better than not having them.  It won't create a mush of distorted sound that is worse than just the arc plus sub straight out of the tv.   

Oops, I see all the responses now.  It sounds like consensus is building that the vanilla arc plus sub is better than poorly positioned ceiling surrounds.  I understand it's personal preference, but consensus seems to be save my money and stay with what I've got (which is quite solid).   Thanks again for the comments. 

The Arc actually provides atmos audio content on their own.  It has upfiring and siding firing speakers designed to bounce off the walls to the seating area, same as the Era 300.  Adding Era 300s would make it ‘more better’ atmos, but that’s even more dependent on placement of the speakers.

For my setup, I have Sonos Ones for surround pretty much right behind the couch.I have the relative volume set low so it’s not overpowering the front speakers.

HI @Randy Rattlesnake 

Not to muddy the waters so to speak….but...IMO...using overhead speakers for surround is not necessarily a deal breaker.  Check the diagram below and the link to Peter Pee. Of course it may require moving the seating forward a bit. You may want to consult a pro-installer for home theater for correct speaker positioning.  FYI, the diagram is taken from the Product Guide for Sonos in Ceiling Speakers by Sonance found on the Sonos website under FAQ’s..  I assume you know the speakers also require a Sonos Amp. 

1 is not a true statement. Sonos has zero knowledge if the ‘support / surround‘ speakers are placed in a wall, in the ceiling, or in your car. They can not be height effect speakers, Sonos reserves that for the extra internal speakers of the Era 300, relying on bouncing the audio off the ceiling. 

2 is also problematic. Sonos has no function for combining ceiling and wall speakers, as indicated in the previous paragraph.