I don’t personally use Sky products, but is it ‘perhaps’ the audio is encoded in the Dolby Digital Plus format (with/without Atmos) and that your TV does not support that codec? What TV is it?

Have you checked the audio output and tried switching the Sky Q box to output its audio in a different format to see if it makes a difference.

Did you sort this as I have exactly the same problem - I can get audio if I change my sky q box from Dolby digital plus back to Dolby digital.  

What TV is it and are you using a HDMI-ARC, HDMI-eARC, or Optical connection (using the supplied adapter) from the TV to your Sonos Arc?

I am using HDMI ARC with my Samsung TV.  I have run the HDMI lead from the Sonos arc into the connection box that has the HDMI ARC connection - the hdmi lead from my sky q box goes into the same box 

On my sky Q box I can select Dolby digital plus and it all works until I play a UHD recording or select a uhd channel 

@CLEAVE,

I would perhaps check either your Samsung TV user manual, or maybe check its full spec. online at rtings.com, if your TV model is listed in their database, as it may not support Dolby Digital Plus pass through via its ports and is limited to the older Dolby Digital codecs only.

Hi Ken this is what I have located

Yes, @CLEAVE it seems there is no DD+ support on your Samsung TV, so you will need to use Dolby Digital 5.1 instead.