Hi i had this same issue with sky and ps4 and i bought this from amazon

HDMI Converter 3x1 HDMI Switch with Audio Extractor Analog Optical Toslink SPDIF Output Support 4K 3D with IR Remote HDMI Cable USB Cable 3.5mm Male to 2 RCA Female Cable for Blu-ray DVD PS4 TV Etc https://www.amazon.co.uk/dp/B073TXX3KV/ref=cm_sw_r_cp_api_i_XJt6Eb7N2R1X9

Plug all your sources into it and plug the beam into the toslink out then plug the hdmi out into your tv this solved all my issues also make sure to set lip sync settings on your tv and in the sonos app to 0

@Pmc ,    I successfully got the optical to work.  

Here’s my post from a few months back.  I see you are in UK.  So I don’t know if J-Tech is on the Amazon UK site.

https://en.community.sonos.com/setting-up-sonos-228990/hdmi-splitter-options-for-beam-6828211?postid=16383002#post16383002

Here’s the product.

I have  a.) Cable Box Optical → Optical switch input

           b.) TV Optical (for TV apps) → Optical switch input

           c.) Optical switch Output → Sonos Optical/HDMI adapter → Beam.     

           Connections a, b, c are using optical Toslink cable. until it gets to the optical/hdmi adapter.

https://jtechdigital.com/product/spdif-toslink-3x1/

Both great options for the Beam, but sadly not so good for the Arc as Dolby Atmos does not work through optical cable.

I have bought a Samsung TV and was hoping to upgrade the Beam to a Dolby Atmos Arc. The arcHDMI direct from TV to Beam sadly causes lip sync problems where the Video is ahead of the audio. So I will continue to use my three into one Optical switch box so that audio is routed from either TV, SKYQ, or Bluray direct into Beam and 2X Ones surround, and not now purchasing the Arc Soundbar. 

FYI, I just spent 1.5 hrs online with Samsung support.  I really kept my patience while I described problem and they had me go through all their steps.  I had not tried the HDMI-ARC port for several months, since the Optical was ‘working’.  But I want to be able to get the features that are supposed to work with the TV.   I am just honestly surprised that at no time, do they seem to be aware of the issue.  Or, they don’t let on.   I even mentioned on their own forum many people have indicated the problem.  In any case, at the end of the process, they’re going to send a technician out.  I have little hope of that.  But who knows.  I even tried different HDMI cables to see if that could be it although another posting indicated to me that probably was not the problem.

There is a new Cable box with Xfinity (U.S.) that will generate 4K.  But it only has one HDMI output and no Optical Output.  Therefore, I would need to add a audio optical extracter splitter, that would then have to go to my existing Optical switch.  

I’m not in any hurry, so I’ll wait for that step.

Hi Michael,

thanks for your reply. Hope your engineer can sort things out. If he/she does please would you let us all know, if you can, what he did to sort the problem out. 
Maybe if he can’t sort things out at least the engineer can advise R and D about the issue.