Hello,
Aravisian actually commented on this in another post: Zorin Lite 17.3 macbook air 2011 high cpu + fan - #124 by Aravisian
I could help later on with the sound as I believe my Macbook Pro has the same audio chipset than your imac. In the meantime, plugin a speaker or headphone via usb (even using jack to usb adaptor) or Bluetooth should work.
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