The Windows and Mac OS X drivers can translate the HID signals to MIDI, but this is not available on GNU/Linux. From the page: "Native Instruments' newer DJ controllers are USB HID class compliant devices. Native Instruments' controllers do not use MIDI. Mixxx does have a MIDI Learn Wizard but it is only for MIDI. I also made Crossfade GNU/Linux, a GNU/Linux distribution for booting from USB drives and DJing with Mixxx. I am not a Mixxx developer but I've been contributing bug reports/feature requests rewriting, organizing, and updating the wiki helping users on the forum making a mapping for my Electrix Tweaker and fixing small bugs that don't require knowing C++ (the programming language that Mixxx is written in). Post your mapping on the Mixxx forum and/or make a pull request on GitHub and your mapping could be included in the next Mixxx release.
See the wiki for more details on how to make mappings. For jog wheels and advanced functions, you can write JavaScript to make your controller do just about anything with Mixxx such as turning a 2 deck controller into a 4 deck controller. If you want to make a mapping, get Mixxx 1.12 beta and try it out. Among many improvements and new features, the GUI mapping interface is now easier to use than ever. We are getting ready for a big release of version 1.12 after more than two years of development. You can help us fix that by contributing a mapping for your controller. As you can see, most of the mappings for Mixxx are for controllers that have been discontinued. We can only make mappings for hardware that we have. Mixxx is cross-platform DJ free ( as in artistic freedom and price) software for GNU/Linux, Mac OS X, and Windows developed by an international community of volunteers. Linux compatibility for sound cards is noted too. It also lists prices and brief descriptions of controllers so it can be used as a shopping guide. It lists whether controllers have mappings for Mixxx and technical specifications for sound cards, both stand alone sound cards and those integrated into controllers. I recent spent a couple days updating the Mixxx DJ Hardware Guide with lists of controllers and sound cards.