Seriously? I mean the integrated ones can also handle 24bits upto 48Khz, and this is digital equipment we are talking about....so where exactly does the extra "quality" come from?? Better noise suppression and filtering??
First off, understand how audio works: At some point, the digital sound file on the PC is going to be converted to analog. This can be done by a soundcard, digital receiver, or stand alone DAC.
Whatever device does this conversion is going to have the biggest impact on overall audio quality. For example, if you have a DAC handle converting the audio, soundcards aren't going to have a big huge impact, beacuse you only get the benefits of the soundcards driver layer. If you have the soundcard output direct via analog however, thats where soundcards make a HUGE difference.
Bit rate/sample rate don't make a huge impact in quality overall; harmonic distortion, SnR, correct reproduction of low/mids/highs, and even the specific tuning of various components on the hardware can have a significant impact on how the audio sounds. Replacing a single opamp (which some soundcards allow) can affect the specific sound signature to a significant degree.
Point being: Onboard is flat, muddles the different audio cues together, doesn't have punchy bass, does poor at the high frequency range, and is very inconsistent in the mids. Aside from that, I guess its "ok".
As for cables, its very unlikely you'd notice any difference. In theory, gold would be "better", but I doubt the difference would be distinguishable except on a pair of top tier, $10k headphones.