Unfortunately soundcards dont have as good s/n as external DACs for stereo.
Its better to have an external stereo DAC and a good enough solution for surround
The good pro ones do. Remember these are the things actually being used to record and mix the music you listen to, any noise/distortion they have you are getting on your music anyhow. They are external DACs (and ADCs), just more than one in a rack. That aside, pro interfaces are often multi-channel digital affairs as well, that you can hook to other DACs.
My point was just that the solution for high end computer audio, including surround, is pro interfaces. That's just not what all of us are looking for, we just want to use our AVRs/prepros .