Reply to Using CDJs in HID mode with added controller

I wonder if anyone has any experience with regard to the following issue:

I wanted to run Traktor with CDJs in HID mode, meaning that the CDJs would act as deck controllers and an aggregated sound card for Traktor. However, due to the external mixer being somewhat limited in control, I wanted to add to the setup my A&H XONE K2 midi controller. Normally using multiple midi controllers should not be an issue as long as the OUT and IN in Traktor's device manager are correctly set for each controller. But in this particular case, the K2 did not even show up as a usable device along the two CDJs in the device manager. The workaround was to map some of the K2's functions onto my computer keyboard, but it is far from a satisfying solution.

Any ideas as to why the K2 was not usable alongside the CDJs?