you missed one option.
pc speaker out to amps.
what kind of 'good quality sound' are you talking about? are you interested using the system in sound quality competitions?
in most cases, if the onboard won't provide decent enough quality, a soundcard will usually do the trick-- all while staying in the analog realm..
a good install---no matter if it uses a head unit, or pc, should not have any buzzing/humming in the audio signal.period. if it does, something is wrong--typically the wiring...
(i am running a full active setup off my pc that is just as good sq-wise as any hu, but with way more tuning options.)