The sound card will make no difference if you are going to an external DAC. That's the point, to bypass the sound card. Digital or USB can sound great with a good cable.
I have a PC, and I love iTunes. What next?
As I read through these threads, I see a lot of folks who think iTunes from a PC into a DAC with a USB cable is mid-fi at best. I've looked at some other formats (foobar and others), and they just can't beat iTunes for convenience and play options. I will have my PS Audio Digital Link iii next week. Am I going to be disappointed? Will a better sound card make a difference?