You can use 2 Traktor decks as Live Input decks and play audio through them but you will need Traktor running and to honest this is not a good solution.
As you already have a soundcard in the S4 I'd look at mixers. Just get something small with enough ins/out. You can get a powered mixer that has an amp built in but as you have active monitors you don't need an amp.
Make sure to look for mixers with lots of stereo inputs not just XLR inputs.
I have an Allen & Heath Zed 14. Not cheap but a good model to compare for features.
I had 2 x Traktor systems (S4 on its own / S4 with decks), desktop PC, Mac Mini running into the mixer and out back into the Mac.
...but then I got bored and sold stuff to buy more guitar FX pedals
Cheers for your replies guys, I'll just plug in the monitors through my S4 at first.
However I've come to another question in regard to the monitors now.
I was inclined to buy the Nubert Nu-Pro A20 but've now seen the KRK RP 8 G3 which are at a similar prive level (arnd 250€ here).
Which one would you prefer for just DJing and MAYBE upgrading to producing at some point. Does any of those 2 have the capability of being okish for producing or would you recommend a 3rd, different monitor?
Thx so much
Thanks a lot for your replies guys. I will start with using the monitors with my S4 integrated soundcard.
However I will buy the KRK RP8 G3's instead of the Nuberts. Do you think this is a good choice?
How do I plug them into my S4? I just checked the output slots, and it only has an MAIN OUT with 1 cinch slot for red/white and one for a guitar-cable (dont know exactly how it's called in english)
Do I need some kind of hub or anything?
Appreciate ur help
They are balanced 1/4" TRS outputs. Use two stereo 1/4" cables to connect the KRKs to the S4.
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