To change SYNC SOURCE it is important that audio is not streaming to the interface. The method for changing Sync Source varies by connection method:
USB – First disconnect USB from the Aurora, then set your SYNC SOURCE, then re-connect the USB cable.
Thunderbolt – Set the SYNC SOURCE from the Lynx Mixer application, or from the Aurora(n) Function > Clock Setup page
LT-HD – The Sync Source should be selected form the ProTools Hardware Setup page or from the Avid Core Audio/ASIO Manager.
Dante – Typically it is best to keep the SYNC SOURCE set to “Dante”. If you change it to “Internal” or “Word clock” make sure and select “Enable Sync to External” and “Preferred Master” next to Aurora in the CLOCK STATUS page within Dante Controller.