Every sound cards are integrated onto the motherboard. The difference with the Dell is that this last has a pre-installed software that optimise performances of the sound card. You can get the same software after your buying for ( I think ) every sound card.

A cheap sound card cannot slow down performances. Only the sound will be worse than another.

Even if you have the best sound card, if you don't have appropriate speakers, it will be a wast of money.

On my Inspiron 6400, the sound is clear and good ( I'm a fan of music. I know what is good or not ).