Select Polycom CX300 under the Input tab.
Open your Sound control panel from System Preferences. Here is the small guide they provide there: I was also able to find this link that could help you with using your current headset.
After a bit of research, I was able to find out that the CX300 R2 should work as well if you are looking for a deskphone for your Mac. The best way to find a headset that works for Mac would be to google it or in Amazon since all these headsets should work for Skype for Business as well. Thank you for stating your situation, my name is Victor, a Skype and Microsoft Office Independent Adviser and also a consumer of these products.
