As a musician, I have always disliked OnBoard Audio - It sucks.
Well, for some gamers it will be okay, but if U have a good amp/speakers (And I am NOT talking about all the shitty plastic speakers out there!!) You´ll almost always hear some kind of static - even with the digital connections.
Remember: Onboard Audio is only a intermidiate/cheap solution.
If you are serious about the sound, shut the OnBoard Audio OFF OFF OFF (In the BIOS, normally), and buy a more descent soundcard! (40-50$ and up should do...)
With all this said, I think AOpen is one of the only companies TRYING to make good OnBoard Audio. I can´t remember the model, but they have/had a MoBo with VERY good capacitors and a ECC83 VALVETUBE in the output stage....Yes!
A ECC83 - just like an old Guitaramp... Amazing! I´d like to hear that one day....