There haven't been any known issues with call quality on Mac Os clients as far as i know so you we may need some information regarding the issue on order to be able to advise. Is the issue on a specific machine? Is the client local or remote to the server? What version is the PBX and what version is the client you are using? What codecs are you using?
I am running v15.5 with all remote extensions and the extensions are the latest 3cx softphone version using PCMU or PCMA codecs. I have 2 extensions only running Mac versions of the software and both simply cannot hear or be heard when placing or receiving calls. Sound chopped, low volume, many different issues.
I have tried many different settings, PBX deliver audio.
No issues with remote phones or Windows / Android applications even on Wi-Fi or 4G
Other software's are not an option since the remote locations has NAT issues and need the tunnel.
I am guessing you have some type of headset attached to the Mac. If so please make sure that the correct settings are selected in the audio preferences of the client. Also try removing the headsets entirely and use the Mac's build in speakers and mic and see if that makes any difference. You can also try other headsets as well if available.