What would be giving out the most audio quality? Outputting to an AV receiver, a single HDMI cable from the graphics card (providing both audio and video information) to the AV receiver seems the more convenient.
However, is there really an advantage, quality-wise, choosing the audio to be output through the audio card, instead? Keep in mind that the discussion is to be a theoretical one, therefore it could be assumed that the hardware used to be the best. Even, graphics-card technologies to be released years from now on could be taken into account.
Share your opinions, and let that knowledge of yours pouring out through every one of your holes!
i have an integrated soundcard on my $300 asus rampage III motherboard and a gtx470. currently i have a direct DVI to HDMI from the pc to my $1200 sound sytem (receiver, 5 speakers, sub) and it sounds perfectly fine to me.
i've used dedicated soundcards and integrated soundcards in the past on the same set of speakers and really there isnt a whole lot of difference unless you are running crap to start with. unless you need the options a dedicated soundcard provides, it really isnt required.