Fully depends on the capabilites of your application...
Its fully sufficient to playback all sound coming from Windows Sound system to i.e. AN1/2.
Same thing would happen if you would use a normal soundcard under Windows.

If you use ASIO aware applications like MusciBee player, which can use the RME ASIO driver,
you can configure (if you want, not that there is a strong requirement) to use AN5/6 or AES ...
Whatever you like.

If you want to route signals in your DAW, then you might use up to all of the outputs,
then you would get signals out of every SW Playback channel in the middle row.

And in submix mode for each of the HW outputs you can make the submix that you require by moving the faders
of HW inputs and SW playback channels.

HW inputs is the signal that comes in on an analog or digital input.
SW Playback channel is the signal that comes from WIndows or Applications and they arrive on the channel which has been configured. For this purpose you can configure WDM devices as you require. By this non-ASIO aware Windows Applications can make use of all inputs and outputs.

See also my blog article about this topic: https://www.tonstudio-forum.de/blog/ind … ernal-equi

This picture might also be useful: