There are situations where you may need to use the iD14 MKII headphone output with a different mix, for example for an artist in a separate room using headphones.
To do this open up the iD14 MKII system panel by going too the iD app found in the toolbar.
Then navigate to "View" > "Show System Panel"
Now use the routing matrix to assign the headphone to either the CUE mixes, or the DAW thru option. Please be aware that DAW thru bypasses any volume control on this output, so it could be very loud!
The cue mixes would be used for creating a separate mix in the iD mixer, creating any blend of analogue and digital I/O, for example if you are outputting a click track to the digital 3/4 output in your DAW you can control the volume for this separately to the headphone mix.
The DAW thru option is less relevant, but you could use this if you were creating a separate mix in the DAW instead, however the fact it bypasses the volume control makes the CUE mixes far better suited for this.