Recording with Xone92 and 2 x Xone K2 in Traktor

Over the course of... well, too long, I've tried to record my traktor sets, using a Xone92, two Xone K2 midi-controllers, my MB Pro and KOMPLETE Audio 6 audio interface.

Since the beginning of this venture, I've experienced a constant ground loop noise - a high pitch noise, particularly annoying when cuing. Worst of all is that the interference bleeds onto my recordings and it is close to impossible to manipulate using software. The lengths I have gone through to fix this problem are ridiculous (e.g. trying my setup in three different countries, 5+ different households, different cables, ground loop isolators, service on mixer etc.).

I have always followed the Allen & heath official guidelines on how to connect my gear, by connecting RCA cables from the K2's to the mixer.

However, I just recently came across this video (also in a recently recorded set with Joris Voorn playing on the analogue Model 1) where only the USB, and no RCAs, is connected to the K2. This sparks the main question: How do I replicate this with my setup? How would the connection between the mixer-soundcard-computer look like? What cables would go where? Any help on this is greatly appreciated! Cheers

The K2's audio interface isn't really too nice. In both cases they are using a separate audio interface to feed the mixer and then you can loop back the mixer's record output.

There are a few things you can try before running out for a new interface:
1. Plug your headphones directly to the headphone output on your K2s, is the noise still there? Test this with both units.
2. Grab an Aux RCA cable and plug any other audio source into the mixer and record that. A song playing off your laptop's headphone jack will do
3. Use the master output from your KA6 into a mixer channel and then loop back the recording
4. Similar to 2, use the KA6's master channel on the back along with it's headphone out (using a 1/4 stereo to RCA adaptor or an Aux to RCA along a headphones adaptor) to get 2 channels into the mixer and loop back. This gives you 2 channels to play with and get a longer mix for testing and might be an OK enough setup if you can't afford a new interface right away. Make sure the headphone knob on the KA6 is set all the way to HOST.

This will allow you to identify the source of the noise (I'm betting on the K2s).