To start off with, this is my setup:
- Xone 42
- 2x Xone K2
- Audio 4 DJ

I aggregate the Xone K2s and the Audio 4 DJ (being the clock source) to one device to be able to use the inputs also in Traktor. This totals to:
- OUT 1- 8 (from the K2s)
- OUT 9 - 12 (from the A4DJ)
- IN 1-4 (from the A4DJ)

I then use the aggregated device in both Traktor (2.6.8) and Maschine (1.x) (that are MIDI synched via virtual output) as follows:
- Traktor: OUT 1-8 for decks A-D
- Traktor: OUT 9-10 + IN 1-2 for send effect
- Traktor: IN 3-4 for recording (routed from the Record Out of the Xone 42)
- Maschine: OUT 11-12 back to the Xone 42 as Line B

Problem I am facing is that for starters the sound coming from Maschine (standalone) is popping like crazy and after a few minutes even crashes my MacBook (not even Force Quitting is possible anymore).

Does anyone have some ideas how to get this working?