Sound Card/Audio Interface question

I recently bought a pair of RPK 6's and of course I would like to play music out of them without having to hook up my S4 to them. I was told I need an audio interface to do this.

Would getting an external soundcard such as the Audio 4 DJ or Maya 44 USB accomplish what I would like to do?

I was already looking into getting an external soundcard to help fix the cracks/pops issue with the S4. (Yes Ive turned off wifi and removed battery, but occasionally I still get cracks/pops)

Thanks for your help

bump :/