Grabbing the attention of the person ahead of you while bicycling
You already known the answer (2), but do not seem to care much for it.  The reality is that you are the fastest user on the shared path thus you bear the most responsibility. 

I would suggest


When approaching, slow down to an appropriate speed.
Make an attempt to notify (bell or calling out), even if they have head phones on.
If they do not respond or move, then further adjust your speed and position on the path appropriately to ensure you can safety pass.


Because you are moving faster, you have the most momentum and will therefore inflict the most damage in the event of an accident.  If the other party is unaware of your presence then you bear most of the responsibility here. (A couple weeks ago I attended a multi-use path crash where one user had their face caved in due to the speed of the other user.  You would be surprised the damage that can be inflicted.)

The reason I would call out or ring a bell even if they may not hear you is liability in the event of an accident.  

Finally, it pains me that many complain about the way that some motorist bully cyclists on shared road ways, then go on and do the same to pedestrians or other slower users on shared pathways.