Reply to S4 with extrnal soundcard

I've been reading a bunch of threads slamming the S4 internal sound card so I did a little experiment on my own with my Line 6 UX1. I didn't go through the trouble of connecting my mains but I did compare the headphone outputs and found the UX1 to be more musical (less distortion and overall more pleasing to my ears). I didn't play around with any settings so it's possible I have some gain structures in the S4 that can be tweaked.

I was able to figure out how to go in to the Traktor settings and select the external sound card for the main output, however, when I did that the cue output was disabled on my S4. Does anyone know what I'm doing wrong? I just went in to the audio settings on Traktor and selected my external sound card and the main audio out was routed properly. There's another option for Win Sound card further down the page but it didn't appear to do anything that I could discover.

Any help would be appreciated!