Native Instruments has released the following statement on Apple Mac OS X 10.11 El Capitan Compatibility with their software:

In Mac OS X 10.11, Native Instruments Audio Units plug-ins will not pass the AU validation and will therefore not be available in Logic Pro. The root cause of this issue has been identified and a solution is currently being developed in close contact with Apple.
There are compatibility issues between some older NI devices and Apple’s new operating system. This issue triggers a ‘kernel panic’ — this serious problem will crash the connected computer immediately, resulting in loss of any unsaved work, or serious disruption of a performance.

The following hardware is affected:

• TRAKTOR KONTROL S4 (MK1)
• TRAKTOR KONTROL X1 (MK1)
• TRAKTOR AUDIO 2 (MK1)
• AUDIO 8 DJ
• AUDIO 4 DJ
• AUDIO 2 DJ
• MASCHINE (MK1)
• GUITAR RIG 3 (RIG KONTROL 3 hardware)

There are beta drivers already available that fix this issue. Updated drivers will be released as soon as they have been fully tested on OS X 10.11.