I got a DG and it was absolutely indistinguishable. As far as I know, sound cards are only good for people who need features like a headphone amp or 7.1 surround sound. I've been trying to get someone to do a blind test for a while now, but nobody's yet taken me up on it. If you're willing, TBT, get someone to switch between dedicated sound and the sound card that I assume you have, not telling you which one is on, and see if you can reliably tell the difference.
i used my friends dg 5.1 to listen to my recording of me playing a violin (it was burned on a regular CD in a generic mp3 file @ 320bit rate). on the onboard sound, it sounded normal and nothing out of the ordinary. with a dg 5.1, i can hear a few footsteps in the back because someone walked by the room at the end of the song. i was using a generic pair of apple earbuds. it was also played at the same volume
its not the best comparison i know.
its not too much of a difference but there is a difference.