There's nothing specifically communicated to players to distinguish between instances used for the Source Monitor and ones used for the Program Monitor. Maybe you could describe a scenario where the user would want separate player settings for each?
For our purposes our playmod is used primarily for different types of 3D playback (horizontal or vertical interlaced for passive 3D monitors, Quadbuffered OpenGL for active 3D monitors or Dual Link NVIDIA SDI) - however we do also provide our own 2D playback, as well. Additionally, we support the outputting of the program monitor preview to external monitors via any of the aforementioned configurations. It seems possible that a user would want a different configuration of the above for the source and program monitor(s) - especially as 3D playback can get dodgy on machines of relatively lower processing power. Also, as there is a major visual difference between any of the above configurations, it comes as a bit of a surprise, even to me, when changing the Playback Settings… and all of the monitors jump to a different view, especially when launching the Playback Settings… dialog window from the 'Output' drop-down menu located on the panel of each individual monitor.