Hi Helpstar,
I've returned the machine now for a refund, as Dell were reluctant to give me a replacement and I wasn't happy that the problem seemed to be unresolveable. (I also noticed that the touchpad was loose along the lower edge, which is an acknowledged problem by Dell.) However, I do really like this machine and if I knew that the sound problem could be fixed I would buy it again.
I read the article you provided the link to, and I did reinstall Windows (with support from Dell) on 23 June but that had no impact (I can't remember the version number, but I know it wasn't 2004). However, the issue highlighted in the article could have been the problem as I noticed I had no audio problems when using Google 'Duo' within the Chrome browser. Unfortunately I wasn't aware of the Sound Control Panel change that I could have tried. I did tell the Dell tech all the experiences I had had but they didn't offer that as a suggestion.
One other thing I noticed was that, when in a Zoom meeting, if I switched between
'Speakers / Headphones (Realtek Audio)' and 'Same as System' in the audio "Select a Speaker" option, the audio would be temporarily restored and then go back to being low volume again. This also happened if I switched the selection back again.
The pc BIOS was 'XPS15 9500_1.1.3' and the Audio Driver was Realtek ALC3281.
I don't know the version of Waves Max Pro, and I don't think I made any changes to the installed app.
As I've said, if I can be assured that the problem is a software one, and that a fix is available and can be applied, then I would feel better about re-ordering. I'm sure that many people who have bought this machine would also be using Zoom or Skype at this time as they are the way we are communicating with each other in these strange times, and I wonder if they experienced the same problem.
Thanks for your suggestions.