Your soundcard will make very little difference if you're already running a DAC separately, but since you're not the soundcard can replace any DAC for a fraction of the cost and almost unnoticeable quality difference. Any card would be fine, I used a simple Soundblaster X-fi Titanium with various amps for years before getting a standalone DAC, and when I did eventually cave and get one I barely noticed any improvement at all. Other audiophiles might try to justify spending hundreds more on a DAC for their computer setup, but the returns negligible unless you are willing to spend much much more. It's like buying a $600 audio cable, almost pointless for PC use.
TL;DR a decent soundcard will do the same thing an expensive DAC will.