Gigabyte boards have good onboard sound, indeed better then some older soundcards, but if it's a Sound Blaster, it would be nice to know what model, but if it is anything from a year ago, or so, I would use that instead.
i would go with the live. but it depends on what you listen to. if you play games, definitely go with the live!.. it gives you eax and support for 4 speakers. also, if you listen to music at moderate volume, use the live!.
but if you don't consider yourself an audiophile and don't play music very loud, then there's nothing wrong with the onboard sound, if you have other uses for the live! (sell it, lend it out, put in another comp).