But they can
If you are using a daw you can assign all parts to 1/2 for monitoring a complete mix and parts of a mix to 3/4 or 5/6.
However if listening with headphones you only hear outputs 3/4 or 5/6
But it all depends on how you route the interface with mix control.
Search this forum there are more people who wanted to route their signals to external devices.
So the question is what do you like to do and with what software.
If you do that we all can help you further.