What's the best way to connect headphones to an M803?
One way seems to be to use the external speaker jack on the back of the main unit, but this is only practical with an external speaker and a switched jack for the headphones.
Maybe not easier, but I think the best way is to buy a headset (headphones with mic) for a HAM radio, and connect it to the microphone jack. You might not find one that just plugs in and works, though. You will probably need to change the connector on the headset.