Sonos Beam for cinema/TV - add Play1 or Sonos One in the rear?

When bonded as surround speakers, there is no "lag" associated with the Beam, PLAYBAR or PLAYBASE. It's only when you "group" another room that you have to pay the penalty for processing for synchronization across all other speakers on the 2.4Ghz network.

Ones are slightly newer technology then the PLAY:1. They include the capability of Alexa, with a microphone array. However, as soon as they're bonded as surrounds, I believe that they lose that functionality. I have 2 pairs of PLAY:1s in my home as surround speakers, and they're outstanding. If I were to do it now, I might potentially instead get the Sonos Ones, just in case I decided to move them elsewhere in my home, and they'd then have the Alexa capability. To me, the cost difference is insignificant enough to go with the newer tech.

The have not yet released any software that would use the internal microphones to "tune" the room. There's been some speculation that such a feature might be eventually released, but nothing concrete that I've seen. They do still support the TruePlay tech via an iOS device, however. Fortunately, it's about a 5 minute setup process, so if you don't have an iOS device, it's not terribly onerous to borrow one from a friend for a few minutes, in order to set it up. Once it's set up, you can toggle it on or off. Of course, if you physically move the speakers, you should do it again.

The rears connect to the beam over 5ghz so there won't be any issue with lag.

The Play and One are the same speaker, the latter just has alexa built in and has a slightly different look. Since the beam already has alexa that takes away most of the benefit IMO, with alexa being disabled on the Ones when used as rears with the beam. For rears I always recommend saving money on the Play 1, unless one really cared that much about the aesthetics.

You would be using true play to tune the speakers upon setup, this is done using the Sonos app in conjunction with an iPhone or iPad microphone to analyze the sound.

Worth noting to check that your TV supports HDMI arc. If it doesn't then there is the optical adapter, you would just lose some alexa skills, would need to manually pair your TV remote, and would then need to check if the TV passes 5.1 via optical.

Is there Trueplay one the Play:1?

Will Trueplay adjust the sound on both the Beam and surround speakers, or just the Beam? If all of them, perhaps would it work with a sub as well?

First - it has to be 2 Play speakers in rear (not 1) paired to the Beam.

Both Play:1 and Sonos One will do Trueplay. If not planning on doing anything but pairing with Beam then a pair of Play:1s most likely better choice (since you already have alexa and airplay with the beam)

Trueplay will work with all speakers (including Sonos sub if you add).

Ok. I sit against the back wall. Would the rear-surround work even if they are pretty close? I am thinking of wallmounting them angled slightly downwards.

Would the Playbar outperform the Beam? Price difference doesn't mean that much.

Yes they would work

Playbar better sound

Beam better interface (arc control via hdmi)

The Playbar is better but not enough to justify the extra price IMO, with rears and in a reasonable space the beam setup will come pretty close.

You would also be losing HDMI and airplay on the Playbar (would need to check if your tv passes 5.1 via optical). If you wanted Alexa you would need the Ones as well.

I would do some further research and check it out for yourself before deciding