The SoundBlaster will be a much better option than onboard.
Its a general rule that any SoundCard will be better than any onboard.
There are a small number of exception to the rule, but only small.
This does not also mean that a £2.99 CMedia SoundCard is better than Onboard cos its not.... Pretty much any SoundCard that costs less than a packet of fags, is certainly not going to be any cop.