Sound issues with Zorin OS 18.1 Pro and Apple iMac mid 2014

Good afternoon all,
I am returning to a topic I have raised previously regarding no sound with Zorin 18. I have attached the link to my original post:

With the following settings there is no sound output:


I am using a mid 2014 iMac. If the settings are changed to:

or

Sound is played through one speaker only. It appears to be a driver issue. Has anyone been able to resolve this issue?

Many Thanks
Best regards.