Reply to Traktor Audio 6 or Komplete Audio 6?

This feels like a really noob question to me, but I can't figure it out.

What's the difference between the Traktor Audio 6 vs the Komplete Audio 6?
Why would someone want the TA6 over the KA6?
In what situations would the TA6 be better than the KA6?

Basically, I have 4trak which has a built in sound card so I've never really needed an audio interface. But now I'm going to get a Z1, which has no soundcard, so I would need an audio interface to use headphones, correct?

I'm not really sure which audio interface I should buy. I produce music occasionally, and I have borrowed a friends audio interface in the past if I needed to use a mic.

I'm also going to be purchasing KRK Rokit 8s relatively soon, should this impact my decision of KA6 or TA6?

I'm pretty much completely at a loss when it comes to stuff like soundcards/audio interfaces. I have a pretty basic understanding of Ins/Outs, but for some reason I feel completely lost in this situation.

These questions are really bugging me, so thanks in advance for whoever helps me out.
If this is confusing, or you need something clarified, just ask.