There's no clear-cut metric to use as a guideline if you're shopping for a sound card. Lengthy audiophile reviews are available, but they generally don't offer a quantifiable takeaway if you have a limited point of reference and don't know much about the subject to begin with. I fall into that category.
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips