DJM 900 just became useless after Mac OS X 10.11.1 (El Capitan) update

I accidentally upgraded my personal Macbook to the latest Mac OS version (10.11 El Capitan). Since then, I am unable to use my DJM at all.

I have tried uninstalling / reinstalling the drivers, I have cleaned all the other audio devices that could have interfered (Boom 2, Air Parrot...), and have tried different cables / USB ports or versions of the drivers without success.

In the DJM900nexus Setting Utility, everything looks great: the USB green LED on the mixer is still lit, and if I turn the knobs to select PHONO / CD / USB, the utility reflects these changes instantly. In the Audio MIDI Setup, I do see the mixer in the MIDI window, but not in the Audio window.

Since there is no Pioneer DJM 900 in the list of Audio output devices, I cannot use my mixer to play sound from my laptop (Youtube, Soundcloud...) through the mixer to my speakers.

In Traktor, if I open the Audio settings, I can see that Traktor detects something happening when I plug the mixer: when the mixer is unplugged, built-in audio is selected; but when I plug the mixer, Traktor automatically selects the DJM900 for output, but complains that it is disconnected. This bit is really weird, it seems to react to the connection, but still think the mixer is disconnected.

Now, I know I shouldn't have upgraded so early. It only happened because that nagging Apple pop up was on the top of my screen at a time when I was tired and clicked "OK" without reading... I am hoping there is a workaround or a quickfix I could use to use my mixer despite already using Mac OS X El Capitan.

Is there any solution to my issue, other than downgrading the OS?