Yes. 

Thank you, Airgetiam!

For those who are annoyed by the one word response, TruePlay measures both the output of the speakers, in addition to the response of the ‘room’. So even if TruePlay didn’t automatically go away when you changed the speakers used, you’d need to re do it based on the fact that there were different speakers in the mix. Probably why Sonos chose to have it disappear when you change the speakers in a room. 

Dear friend, 

Absolutely nothing wrong with one word answers!

Thank you again for your prompt expert advice. I will follow it thoroughly when I receive my new Era 300.

Just as an experienced user, I.e I made this mistake before…..be sure to remove your current One SLs as surround speakers before you attempt to add the Era 300s to your system. It will make life easier. 
 

I made the mistake of not removing the Sub and surrounds when I swapped my PLAYBAR for an Arc before, there was a lot of cursing when I figured out what I’d done Easier to do things correctly, in steps. 

Good advice! I had already removed my two ONE SL satellites from the existing system, and added them to another room system (Beam Gen 2, and recently acquired Sub Mini).

I am anticipating that the Arc+Sub gen 2+ Era 300 combo will sound as advertised.

Be well. 

So once I receive the Era 300’s, I will remove the One SL’s as the rear speakers and put the Eras there instead. Can I still use the One SL’s in the same surround sound setup just in a different location, or does sonos limit you to only having so many speakers in one room? I already have the Arc and the Sub(Gen 3).

You’re limited to exactly 2 speakers setup for surround sound.  You cannot have 4 speakers setup for surround sound.  So your Arc + Sub + Era 300s will be your room.  You can setup the One SLs as a separate room.

If one uses the USB-C on one of the Era 300's to connect to a Turntable is the sound played on that ONE Era 300 or both Era 300's or both Era 300 and Arc Soundbar?

Cheers all!!

Unfortunately, due to the configuration as a one way directly linked device, the Line-In feature is disabled when any Sonos device(s) are used as surrounds.  This includes Amp, Five, and Era speakers.

Ahh... got you.. many thanks jgatie.

So I guess it would be a case of dis-engaging the Era 300's as Surrounds in order to play the Line in source. Would the sound then come out of both Era 300's?

Received my pair of Era 300's…

Wow!

They are fantastic! Paired up to my Arc with no problems. Automatically updated firmware and all was good to go 10 minutes after unpacking the Era 300 speakers.

Beautiful surround sound from TV and also from my Qubuz music App! Sublime!

Highly recommended!