Yes, I’m pretty sure the two rear channels are merged with the front. Not everyone has ‘bonded’ surrounds and so switching off the surrounds means the front channels will handle all the audio sent to the HT main player.

If you disable surrounds, the surround content will be played out of the Beam.

Hi Ken, thanks for the answer. Could you explain what you mean by, “not everyone has bonded surrounds” please?

Ok thanks for the answer.

I’d be an example of “no bonded surrounds” I have a Beam in a bedroom where we almost never listen to anything with a surround format so we never bought surrounds for it. 

How would you turn off the surrounds in the Sonos app? In the app I can only see a possibility to turn the volume down to zero. If this is the option you use I do not think the Beam will take over the surround stream.

I’m also curious as to why you’d want to turn them off, since there’s nit much sound coming out.

At the very top of the Surround Audio screen is a toggle for this.

I agree in that if the sound out of the  surrounds is negligible there is little gain in switching them off, and if it is non-negligible you would probably be best advised to let the audio do its thing.

Some people prefer just to have music from in front of them, and would rather turn off the rear volume completely than use ‘Ambient’.   (But I suspect the OP is talking about TV sound, not music.)

I would be very surprised if Sonos with surrounds turned off behaved differently from Sonos with no surrounds, which I think is the point that @Ken_Griffiths was making.  That is, the audio would be ‘transferred’ to the front speakers.  I don’t think I know enough to give that as a 100% guarantee.

@John B I hadn't noticed the toggle, thanks. I would expect sounds to the go through the front speaker only .