Strange Audio Issue on PHT via Mac mini

I've recently started using Plex after using Kodi / XBMC for years.
Basically my issue is that I get no audio once i start playing my media, it can be a movie or series.
Now the intro music when you click into a series works fine, and the clicks as I browse my media I can hear as well. but as soon as i choose and episode and hit play, nothing, the media plays fine but zero audio.
Set up is as follows, PHT running on a late 2014 Mac mini, 16GB RAM, top spec machine.
PMS is running via FreeNAS and serving media from the same place.
It seems if I try play media, my audio dies, cause i tried playing music in iTunes while PHT was open and the audio defaulted to playing from the mac mini speaker and not through my TV connected via HDMI.
When I quit PHT the audio from iTunes plays correctly through my tv
Thanks