No....
That is when you compare the onboard stuff with equivalent soundcards. If you do that, then no, there is no difference at all.
Of course, it speaks for its own that if you have a high classed fancy gold plated 7.1 soundcard and using it together with a super-duper amplifier and a 1000W multi-speaker system that you'll probably have a better sound. But in that case you're not comparing stuff in a fair way.
Onboard sound is in almost all cases extremely good (unless you're a real movie-fanatic or working professionally with sounds, then nothing is good enough
)
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