Reply to S4 low output volume, urgent

I bought a Kontrol S4 and i'm very happy about it, but it has a few problems i really have to get rid off. So normally i use my setup like this: Laptop connected (via output audio jack) to a NSA 2008 Stereo Mixer from JCB, this mixer is connected to the Peavey 260 amplifier and then the volume i get from my JBSystems speakers is loud enough to do a small party. But if i use the setup like this, i can't use my headphones because those work with the soundcard of the s4 which i'm not using.

When i use the setup with my S4 connected directly to my speakers, the volume i get out of my speakers is very low! So that's my problem, i would like to get high volume and i would like to use my heaphones while mixing,

Setup:
P1060622.jpg
Help me,