VCI-100 and Audio controllers

Hi!

I'm new here and also new to the DJ'ing world. I need some advices and help on the things that I would be buying.

I plan on buying the VCI-100(Black Edition) but I am not sure whether I need an audio controller?

I already have a soundcard with 2 outputs (1 for headphone/speakers and the other for SPDIF/Digital out which I use to connect my 5.1 sound system) all running under Asio4ALL driver.

The following are available and I can't seem to compare what differences they have.
1) M Audio Fast Track Pro
2) Vestax VAI-40
3) Native Instruments Audio Kontrol 1

My concerns regarding an audio controllers:
a) would an audio controller improve sound quality?
b) is it worth to spend the extra $200 for it?

I am using Traktor Scratch Pro and its really hard to control it with keyboard, and I don't want to get used to controlling the deck using my keyboard. Heh.

Thanks!