here are some screenies from anandtech wich compare different onboard sound chips .. they have compared onboard creative sb live and karajan also. u can see the difference .. its not much and an onboard sb live will be performing equally as an external sb live 7.1 i guess.
and herez the link to the complete review,
http://www.anandtech.com/mb/showdoc.aspx?i=2465&p=27