Because i don't know how to set it up. When I registered and started my traktor software it did not list the vci-400 as one of the software controllers I could use when I selected vestax from the menu. I dicked with the settings a bit but decided I should hit the forum. I know the answer is probalby already on here but i was unable to uncover it with the search function.
If it helps I bought my traktor copy with the NI2 soundcard.