Hi
If I understand correctly your question, then the answer is: the 3CX Voip Phone supports the same audio devices supported by the operating system; each audio driver installed in the system can be used to play and/or record.
Therefore, if you will check the File/Preferences dialog box, in the "Sound Devices" group, there are three kind of audio events used by the phone - speaking (mic), hearing (play) and ringing(ring). Each such as event can be "routed" to an already installed audio device.
By default, the phone routes all these events to the same, system-default, audio device. But, supposing you have a soundcard and a headset, then you may configure the phone to use for ringing the soundcard audio driver, while for mic/hear the headset audio driver.
Try this and check if it works.
Regards
vali