Not all "onboard" sound devices use more CPU cycles then a card pluged into a PCI slot. The Creative chip on the Gigabyte board is the same chip in the Creative Sound Blaster 128 which is an upgraded version of the origional Ensoniq Audio PCI sound chip which was the first PCI based soundcard by the way. The chip itself does most of the signal processing freeing the CPU for other things.
It makes no difference to the motherboard if a device is soldered to the board or connected through the PCI slot. This goes for soundchips, RAID controllers and anything else that can be put on a PCI card.
You might be thinking of AC97 sound which also has a chip soldered to the motherboard, the difference is this chip does no signal processing but acts as an interconnect to the sound inputs and outputs, all sound processing is done by the software (drivers) which takes CPU cycles.