When you send an AirPlay 2 signal directly to the Beam, it is only going to be stereo, and you won’t be getting a true 5.1 signal. 

This is due to Apple restricting AirPlay 2 signals to stereo only to non-Apple devices. 

So yes, adding an Apple TV to the TV via HDMI would help. You could then play your movies either directly on the Apple TV, or on your Mac, sending thecAirPlay 2 signal to your Apple TV. 

Thanks for your answer but I 'm not sure I understand fully. I did not include enough details about my configuration I believe.

My current setup is my Mac connected with hdmi to my video projector in front of the couch, 3-4 meters from the screen and the Sonos beam. 

I use airplay for the sound to avoid the need for an HDMI splitter and a 5 meters cable to connect to the beam 

I can't quite understand how the appletv box can help if I can't use airplay anyways for 5.1 sound…

Can you clarify please?

You can only get the Sonos speech enhancement feature when connecting to the soundbar over a wired connection - it’s not available over a wireless link. Airplay v2 on Sonos (and other devices) is stereo audio only. See this link:

https://www.whathifi.com/advice/apple-airplay-2-everything-you-need-to-know

To get 5.1 surround sound you need to use a wired A/V connection rather than Airplaying the audio.

Thanks a lot.

So either I need to by an hdmi splitter to wire both the projector and the beam or I need to return the beam and choose a soundbar with an HDMI out. That a pity the beam doesn’t have one...

Note it needs HDMI-ARC/eARC as the input to the projector - HDMI will not work as it needs the audio return channel. The alternative is to use optical and the Sonos optical adapter, but most users  tend to use an extractor/combined switch, such as the examples below… these are the more expensive ones that do Atmos audio, but things are much cheaper if just looking for 5.1 surround sound:

HDFury Arcana (as widely mentioned)

https://www.hdfury.uk/product/hdfury-arcana/

Feintech VAX04101

https://feintech.eu/en/collections/hdmi-topseller/products/feintech-vax04101-hdmi-earc-pass-switch-4x1-for-soundbar

OREI HDA-931 or OREI HDA-935

https://www.orei.com/products/dual-hdmi-earc-audio-extractor-converter-4k-60hz-18g-hdmi-2-0-arc-support-hda-931

https://www.orei.com/products/dual-hdmi-earc-audio-extractor-4k-60hz-with-optical-port-3-5mm-jack-18gbps-bandwidth-hda-935

Ezcoo

https://www.amazon.co.uk/Splitter-Soundbar-Bi-direction-Breakout-HDCP2-2/dp/B0BBZGPT6F

Thanks, and I consider that option, but that goes against one of the reason I have a sonos setup. It’s that it is clean without a bunch of cables.

In addition I need to unplug my sonos music setup which is on S1 in order to be able to use the beam so that’s a lot of cons...

@Tonio44 

Imo it‘s more a question of making some thoughts about a possible setup for my requirements BEFORE buying anything.

If I‘d like to have a ht setup with multichannel audio but won’t be able to do cabled connections, I’ll run against the wall just at the beginning of planning a setup. 
 

Sorry, but many users buy Sonos products and think „wow, they are expensive so they will manage everything“. Later they are disappointed because they realize how things work because of general technical limitations. 

Hi Schlumpf. You may be right on average but your assessment of my situation is incorrect and brings nothing to the conversation. I love my sonos 5 and connect that still perform brilliantly, so don’t be mad if I criticise the beam 

I was simply mislead to think the Airplay compatibility meant it was usable for the main purpose of the beam: listening to multichannel audio.
And fun fact: the beam+ sub is not a particularly expensive option for me since I benefit from the renewal discount. I would have chosen a dedicated system with in and out hdmi ports for the same price if the communication was transparent about airplay. And the fact that the beam only has 1 hdmi port only added to the belief that airplay was a real option. 

Looking at the forums I remembered I solved most problems when I first intalled my old sonos system with static IP on my network and I just did it again and it seems to solve this issue once again :-)

@Tonio44 

Great, you solved the problem of using S1 and S2. 

All the rest said above wasn’t meant in every point to you. And also fine that you are satisfied with the other parts of your system. 
But… 

„…but that goes against one of the reason I have a sonos setup. It’s that it is clean without a bunch of cables.“

…and…

„I was simply mislead to think the Airplay compatibility meant it was usable for the main purpose of the beam: listening to multichannel audio.“

…is what I tried to point out. 
A simple Google search about how Airplay works and a closer look at Beams user manual for multichannel tv audio would be useful, if you’re not sure before how both work in detail. 
But please don’t get me wrong… my intention is not to blame you. Just want to say, how easy such disappointments could be avoided.