Seems like the z1 only has one audio output, so the mixing will be ‘internally’.
I myself have a audio 2 dj (mk1). I mostly use it as a soundcard for my studio though since I don’t use Traktor live. My biggest concern with the mk2 is that it has 3,5mm connection instead of the 6,3mm ones found on the mk1. These are a lot smaller and, by effect, a lot less reliable (easier to pull out accidentally or just snap off).
Also, with an x1 and a z1 you effectively have a full mixer-player setup so basicly with those two little boxes you’re basicly ready for everything, just need to plug an RCA lead in.
Just my opinion though, but I’d go with the z1 if you’re willing to cough up twice as much. And if you’re going for the audio 2, maybe search for a mk1 second hand or so. I really wouldn’t want to rely on those 3,5mm jacks. I also got mine second hand for just 14 Euros.
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