Hi.
Is it possible to listen to Input 3 + 4 via Direct Monitoring with the Outputs 1 + 2 if I use the Komplete Audio 6 MK2?
With the first edition of Komplete Audio 6 this is not possible.
This article should help you to figure it out.
https://support.native-instruments.com/hc/en-us/articles/4409573433361-Using-the-Direct-Monitoring-Feature-on-My-KOMPLETE-AUDIO-Interface
Here is also a nice tip that might be useful to you. :-)