Saw your post from today on this thread:
Sounds like you’re on the right track, however, judging from what I’ve been reading folks have been having nothing but problems trying to get the VCI-300’s sound card to work in anything but Itch. Not even sure if this will be possible to be honest (at least until Vestax address’s what’s intended or going on).
Shame such a beautiful piece of kit has to have so many nuances. 
So this puts you back in the boat of using your Terretec DMX as the sound card of choice in Traktor PRO (which is going to be far superior to the built in VCI device anyhow).
Goto Preferences > Audio > “select your DMX 6Fire driver”. Make SURE it’s not a direct sound or DX version of the driver. Chances are the ASIO version will be tagged with the word ASIO in the driver name, or just something plain like; DMX 6Fire. Trust me, the 10-12ms latency you’ll see will be key compared to the cracks and pops you’ll likely get from running direct sound drivers.
Looking at the DMX unit it appears you have 3 stereo pairs to work with (1/2, 3/4, 5/6), so this should work beautifully. I’m going to assume you’re not mixing externally on a mixer, but instead running all internal.
You’ll ignore the headphone output on the VCI, use the one on your DMX instead. Under Preferences > Output: set channels 1/2 as your master output (L/R) and 3/4 (L/R) as monitor output (your headphone out on the front of the DMX is going to default to the 3/4 or 5/6 stereo pair). You may even have a button to select which one you want assigned to it, test the different stereo pairs in Traktor to figure out which works. Just be sure your cue mix and cue volume in Traktor are balanced so you’re getting output from the master and cue’d deck. If you’re still not hearing anything in the headphones make sure you’ve clicked the CUE button on the deck you’re trying to hear in Traktor (you sound intelligent, doubt this would happen to you =P).
If you’re not seeing all your stereo pairs from the DMX unit in Traktor and only 0/1 or something to that effect, then you’re not selecting the correct driver or there is something wrong with the DMX’s driver implementation.
Get back at me, we’ll worry about mini-translator and jog wheels after this is all working proper. I think Traktor PRO only supports high-def / 14-bit midi messages on the pitch faders, not jogs (thus the need for the translator).