built in soundcards arent designed for professional audio, the Line 6 would give you the same results.
if you are serious about this you could look into an M-Audio box or one of the many other brands of audio interfaces.
if you do a search in the Recording Gear section for M-Audio, Presonus, and Edirol you'll be on your way. The Presonus stuff is plug'n'play on a Mac. no drivers.
have fun!
