To load the mapping, download it, find the .tsi, open Traktor, navigate to Settings(Cog Icon)->Controller Manager->Add->Import TSI->Import Other and select the .tsi file.

edit 1-4-16: aleeway/ablahblah checking in here, will be working on maybe reworking this so it takes less pages and will be more bug free.

edit 1-6-16: v3.0 is up! Deleting the old documentation and uploading revised documentation here. Basically the main things that changed are I removed bleep because it was unstable, adjusted how to access beginning of the track, and reworked how to enter super filter mode.

A word of warning. Avoid pressing more than 3 buttons at once on the Mixtrack. It can occasionally handle it depending on which buttons you are pressing, but in general, this is still a pretty cheap controller. It can and will ghost on you, i.e. if you press too many at once it will press trigger keys at random without you expecting it, so be careful.

Decks Overview:

Hotcue buttons 1,2,3 access hotcues 2,3,4 respectively. 1 is inaccessible because it usually sets your beatgrid. Hold Delete and press a hotcue to delete.

The middle FX knob controls dry/wet. The Effect button and right FX knob control the FX button and a knob. You select which FX button/knob pair this controls by pressing down the left FX knob (Select). The hotcues buttons will light up to indicate a transition to pairs 1, 2, or 3. If you are in Group Mode, you can kill all effects (Buttons all unpressed, D/W reset to 0) by holding the Select knob down and pressing the Effect button. If you are in Group Mode, you can turn the unit on or off instead by holding the Select knob and pressing the Effect button. Bear in mind that if you hold the Select knob and hit Effect, it will immediately exit selection mode and will not transition to the next pair. i.e. if you are using button and knob 2, and you hold Select and press Effect to kill, you will still be using button and knob 2 (it will not transition to 3, possibly saving you from having to cycle through and reselect 2). i.e. if you are using single mode and you toggle the unit on, you need to release Select and press Effect again to toggle it off (the Effect button only switches the unit on/off if you are in selection mode, which you just exited by pressing Effect, I know, somewhat contradictory).

You control FX assignments for each deck with the Tempo Bend buttons. (-) toggles FX1, (+) toggles FX2.

Your loop controls are pretty standard, I think I may have flipped the order. If Mode is unlit, you're in autoloop mode, if it is lit, you're in manual loop mode. One interesting thing is that if go to manual loop mode and press Loop In or Loop Out while mid-loop, you can now use the Jogwheel to manually adjust your Loop In and Out.

If you hold down the Mode button, you get access to basically preparation features, namely beatgrid, seek, pitchfader range, and full Sync. Pressing and releasing Reloop/2X now deletes hotcue 1 (grid) and sets it, respectively. Pressing Out/1 Bar will tell Traktor to autogrid your track (handy if your grid is off and you can't move to the beginning to reset your grid). In/1/2 will copy beatgrid phase from tempo master. Here's a usage scenario to make that last one make sense; you're mixing Deck B into Deck A. You realize that Deck B has the correct BPM, but the beatgrid is offset a bit in one direction. You can quickly fix it by beatmatching with Deck A so they are audibly sync'd, then set Deck A as Tempo Master and copy phase from tempo master to Deck B to automagically fix its beatgrid.

If you hold down Mode, pressing Keylock will also toggle through tempo fader sensitivity. It'd be a good idea to have Pitchfader Sensitivity visible in your Deck Headers (Settings->Track Decks->Deck Headers). Pressing once will queue 4% sensitivity and will turn the LED off, pressing again triggers 8% sensitivity and turns the LED on, pressing again triggers 16% and turns it off, pressing it again cycles it back to 4% (LED still off!). This order and LED order is always respected; you can quickly switch your sensitivity like this, technically you could do it without the deck header actually.

If you hold down Mode, the jogwheel will also do a quantized 4 beat Move. You can use this to quickly seek through your track when you first load it in; i.e. to quickly find the break. Additionally, if you press Cue, this will jump you to the beginning of the track, and if you press Sync, this toggles full deck Sync on or Off. By default, Sync just does a Tempo Sync.

If you do any of the actions I just mentioned when you hold down Mode, it will not transition between Auto and Manual loop modes. It'll just return back to the mode it came from.

Play/Pause and Stutter (aka Cue Play) function as normal.

Holding Scratch turns on Flux Mode (hold, not a toggle). You can backspin or call a hotcue and it will return as if you never did. One limitation is that you cannot pause the track or cue play and expect it to return, it's a limitation on Traktor's part. I removed bleep from here because it got a bit unstable sometimes, it may make a return in the future. Additionally, you should know you set a normal loop and expect it to return in Flux Mode....which is why the loop buttons are now Loop Roll triggers :). Mode is 1/8, In/1/2 is 1/4, Out/1Bar is 1/2, Reloop/2x is 1. The loop roller possess full memory so it will adaptively remember what order you pressed and released the buttons. Have a look at the Loop Roller mapping if you want to see some magic happen in the Modifiers :). Remember, pressing down more than 3 buttons gets risky with this controller though.

Mixer Overview:

The shift buttons here are Back and pressing down the Browse knob.

Treble, Mid, and Bass are as normal, initially. They are all on soft takeovers because they can get reassigned in this mapping.

Channel faders are totally normal. Crossfader is totally normal.

The Master Gain fader no longer does that. I keep bumping into it with the channel faders, and that's a really scary proposition. Instead, it now controls your crossfader curve.

Master Gain is now handled by Cue Gain (should also be soft takeover). Cue Mix is still handled by Cue Mix.

Load A, Load B, and headphone cues are initially as normal.

Browse knob initially does Tree browsing. Press it down and see the Folder LED light up to indicate it is now doing Folder browsing. The File LED doesn't help you here because I have it assigned somewhere else, just use the Folder LED.

If you hold Browse, the Cue buttons change to adjust and reflect Snap and Quantize.

If you hold Back, the Load buttons now duplicate the deck opposite the one you pressed. i.e. if you hold Back and press Load B, it will duplicate Deck A to B, and vice versa.

If you hold Back and press a cue button, it will change to display the very top of the VU meter, pre-fader. Think of it like a Signal LED on an audio interface. Additionally, while this mode is active, that channel's High EQ knob will change to adjust Channel Gain. You can feasibly check and set Channel Gain like this. If you press the same cue button twice, this will also attempt to set that channel as the Master. Remember, the way Traktor works, the deck needs to be playing to be set to Master.

You can change the Mid EQ knob to control bass and the Bass EQ knob to control Filter by holding Browse and pressing Back, or holding Back and pressing Browse. The File LED will light up to tell you this mode is active. Bear in mind the filter will always force on in this mapping, and remember that the knobs are on soft takeover. Be aware of where your filter is; it's possible to put the filter down, exit to change your Mid EQ setting, and forget to go back and put the filter back to neutral! Random protip; the Ladder filter option in the Settings->Mixer->EQ/Filter Selection has some nice resonance to it.

That pretty much does it for this mapping. It's still kind of in a perpetual beta test, as the mapping is so huge, I can't really check for full stability without a bunch of people going out and testing it. There's a lot of redundancy built in, so it shouldn't be too bad if something glitches, but please please please let me know if you find a bug. Would I consider running around with a Mixtrack with this mapping though? Actually...even given my PL1s, I would think about it. This includes a whole bunch of prerequisite features I personally want in a controller.

Example, pretty feature intense usage scenario:

Track is playing in Deck A. Load a track into Deck B. Realize Traktor didn't analyze properly. Hold Loop Mode, seek to the break, press Play. Hold Back, press Cue to see the channel level, set Gain using the High EQ. Release Back, put the High EQ knob back. Realize Beat Grid is off. Hold Loop Mode, press Cue to jump to beginning of track. Release Loop Mode, jog to first beat. Hold Loop Mode, press Reloop/2X to reset Beatgrid. Continue holding Loop Mode and seek to where I want to begin the track. Use Headphone Cue and Cue Mix to audibly confirm.  Use the (+) button to assign FX Unit 2 to Deck B, program an effect in using the Select knob to cycle through effect settings. Adjust crossfader curve (now assigned to Master Gain fader) to a fast cut. Start Deck B in time, and cut it in using the crossfader. Realize that you done goofed Deck B is not BPM sync'd. Quickly hold Loop Mode, press keylock twice to set 8% pitchfader sensitivity, and fader-ride Deck B so it is in time. Transition is accomplished! Press Back and Browse to select Filter mode, put a Reverb on Deck A, hold Scratch and Loop Roll Deck A 1/2, 1/4, 1/8, and filter down to take it out of the mix :)

Changelog
v1.0.0 - initial release
v1.0.1 - swapped D/W and effect param knobs as per a user request
v1.8.0 - Fixed some Loop Roller limitations, and put soft takeover on most control knobs (you must match the software positions on the mixer before the mixer does anything). Also desensitized the platter quite a bit, found that the past sensitivity made beatmatching really difficult actually. Loop roller still has no memory function though.
v1.8.1 - Bug fix, I uploaded the wrong version and Super Filter entry was glitched. Updated now.
v1.8.2 - Made the mapping smaller, consolidated Mixer into Primary mapping. Consolidated Hotcues into one mapping. Fixed some added missing soft takeovers. Most importantly, there is now an emergency reset for the FX LED mod. If you switch to Single FX, and press down the clicky knob, the variables that control the LEDs will reset, in case your computer hangs and the LEDs get out of sync.
v2.0.0 - FINISHED Loop Roll functionality. Please run it around its paces, I'm still trying to figure out if there are any bugs, but so far it looks good. I also pulled out Mixer and put it into its own mapping again, may be doing some more things to update that in the future. ALSO, I added a Bleep button! Similar to Serato's functionality, where you can Shift-Press the reverse button to temporarily reverse the record in slip mode and "censor" any profanity from your tracks. Press Shift-Play on your Mixtrack now to do it.
v2.0.1 - Had some extra mappings loaded in the uploaded version, cleaned those up and reuploaded.
v2.0.2 - Fixed a bug with the bleep feature that could let the song get permanently stuck on reverse. (Made it so that releasing the shift button will automatically bring the song back to normal operation.)

v3.0.0 - Large rework. 8 mapping pages condensed down to 3 pages. More redundancies added, some unstable features removed.