Mobo sound or extra sound card

Hi all,

This is probably a really DUMB question.

I'm going to get an ASUS P4C800 which has sound onboard (build in sound card I presume) It's labelled as 6 channel.

I run my current PC's sound via taking a standard headphone jack and splitting that into 2 RCA's which then go into my HifI through my Bose.

Now the question is ...... I see most after market sound cards only have line out's and not actual RCA output's so I would have to use a line splitter anyway.

Is it worth my getting a £25 Creative sound card to take some strain away from the Mobo ? Or is it an utter waste ?

I have seen their are external sound cards (boxes) that run through the USB ... should these be avoided ?

Cheers all.
ThanX