Do not  factory reset. 

https://support.sonos.com/en-us/article/add-surround-speakers-to-a-sonos-home-theater

To add the Era 300s as surrounds, you have to separate them as a stereo pair first, then select the “Set up Surrounds” option under the Arc settings in the Sonos app.

To use the Era 300s as a stereo pair again, you select the “Remove Surrounds” option under the Arc settings. Then you set the Era 300s up as a stereo pair again.

Each time you switch to surrounds or to a stereo pair, you will lose any saved Trueplay tuning. But you do NOT need to perform a factory reset.

Thank you.

It would be outstanding if Sonos would implement an easy switch between stereo and surround without having to retune.  My room setup has chairs that can simply be turned around and face the speakers when I want to listen to music

Two wildly different connections. One as peer speakers (the normal stereo) connected to your Wi-Fi, the other a ‘child’ relationship connected to the sound bar. My guess is the nature of switching between those two things is both not easy, and not ‘quick’, which may be why Sonos engineers haven’t done it, despite requests from the very beginning when Sonos initially released the sound bar with surrounds concept with the PLAYBAR. 

Good evening everyone!

I'm new here and I apologize if this question has already been asked. I treated myself to a system with a Beam 2, a Sub Mini, and 2 Era 300 speakers that I configured as surround. I've done a few tests with Dolby Atmos movies, and the Era 300's rendering is often bluffing.

On the other hand, what I find very frustrating is that most of the time, if I'm watching non-Dolby Atmos content, such as a TV channel or a sports match, the Era 300 speakers are virtually silent, the sound only coming from the soundbar. I notice that they send out sound but at a ridiculous volume compared with what they send out if there's Dolby Atmos.

I've tried forcing the volume of the surround speakers in the settings, but it doesn't make any difference. Does anyone have a suggestion for making the 2 Era 300 surround speakers more present so as to constantly have the impression of being surrounded by the speakers? Thank you!

Sadly the producer of the content controls what sound is sent to which channel and the volume levels.

Cranking the Sonos settings can only make what the producer has placed there louder.

What sound format is Sonos saying it’s playing when you notice this?

Dolby 5.1

Sonos has chosen to not have the inside speakers of the Era 300 on when non Atmos content is being played. This could be the reason the speakers seem less loud, though they should be within spec for 5.1. 

I also have this setup and being an avid music lover, I would also like Sonos to implement a quick switch between stereo and child-surround mode. I do not believe it is not possible. EVEN keeping the tuning. Every thing is possible. Learnt it through my journey coding.

Everything is possible if someone is willing to pay for it.

Learned that from my journey through coding project management.

Hi @jgatie & @Jonescifer 

I have removed several of your posts. Please refrain from antagonising each other.

Sonos should update their software to activate the inside speakers on the Era 300 when 5.1 audio is being played and de-active them when Dolby Atmos is being played.  That really shouldn’t be that hard for them to implement in their software.

5.1 audio is designed for front firing speakers so to route rear channels to side & up firing speakers on the Era 300 is doing 5.1 audio a disservice.  Now for audio formats with more than 5 channels and audio formats that contain height channels...  That’s a different story and I completely understand why the Era 300 would use side and up firing speakers.

I personally am holding off buying Era 300’s for surrounds because the majority of the content out there to watch is in 5.1.  There are relatively few movies / shows in Dolby Atmos compared to what’s available in 5.1.  So, while I’m sure the Era 300 would be awesome for Dolby Atmos content.  My Play 1’s are likely better for 5.1 content (Based on opinions from owners of both the Era 300 and Play 1 where both have been used for surrounds in a A/B comparison).

I could not agree more. Here I sit, with money in my pocket, wanting to buy a better surround/atmos combination set of speakers to replace my SL Ones. But, after months of waiting, we hear nothing from Sonos. I guess I will wait some more, until a “2” or a “4” speaker is introduced with this magic switch.

I have a Setup consisting of an Arc, Sub Gen. 3 and two Era 300s. Before using the Era 300s as a Stereo Pair only for Music I had them as Rear Speakers in a Surround Sound Setup. It wasn‘t bad for music at all, it actually sounded gread. BUT when I used the Era 300s as a Stereo Pair for listening to music they were on a whole other level (Dolby Atmos and regular music content on Apple Music). It would be awesome if the Era 300 as Rear Speakers could sound as great as they do as a stereo pair when listening to music. They‘re clearly capable of doing so and as I‘ve read many people in the Sonos community want that. Is there something planned, Sonos?

Thank you for listening to your Customers and putting out great, simple to use products!

This is sort of my take on the matter, but I think my reasoning is slightly different.  Say you have two rooms you want audio to play in, one of them is home theatre, and these are the speakers you have to work with.

Arc

2 subs

2 Era 300s

2 Sonos Ones

You can set them up with option A

Room 1 - Arc + sub + 2 300s

Room 2 - 2 Ones + sub

or Option B

Room 1 - Arc + sub + 2 Ones 

Room 2 - 2 300s + sub

I choose option B, because I want 2 atmos rooms.  When the rooms are grouped, I’m not forced down to stereo as they would be in option A.  The HT room is not quite as good with option  B for atmos, but it’s still really good.  For music/stereo sources, room 1 is at least the same for both options, while room 2 is definitely improved for option B.

I honestly didn’t even try option A, because the appeal of option B was too great.  As well, it leaves me a bit of room for future upgrades if Sonos comes out with another atmos capable speaker in the future that is better or worse than the Era 300.