I'm new to this too. May I ask what is the purpose of the sound card then? Is a sound card not required to make the most out of the Astro A50?
Back to basics: Audio is an analog signal. On the PC, the audio file is saved as a digital file. What that means, is at some point, some device is going to convert that digital file into an analog signal so your speakers/headphones can output the sound.
When you use the digital output of a soundcard, this process is handed off to some other device. In this case, the A50's, not the soundcard, will be the primary driver of audio quality. You only benefit from a soundcards software side enhancements. That's it.