Not all SoundCards are better than OnBoard at all.
There are some great onboard options out there and there are some really poor soundCards out there too!
The ONLY exceptions are the Asus and the Creative ones...
Those cards you can get for a tenner for example are a total aste of time and are really only any use for a basic internet PC that has a dead onboard option, or a really old PC that you can no longer find drivers for, other than that, they are pap at best,
I honestly cannot comment on your Particular onboard option, but I can safely say with complete honesty that some of my boards have fantastic onboard audio, quite possibly some are better than a basic SoundBlaster live or Audigy but at the same time as saying that, NONE are using their onboard option withj the exception of only one... Thats my Gigabyte GA78M-DS3 and thats only because it seems to go well with my Amp & Speakers so I never bothered to put another card in.
All other boards have Creative or Asus