Virtually any sli capable Z77 motherboard will do the job for you.
They will all have X16 capability for a single slot, and X8/X8 capability in sli. It is part/limitation of the chipset design.
But, do not worry about X8/X8. Even with a card as good as a GTX680, there is negligible difference in actual FPS. Think 1-2% or so.
As to the audio quality, I have no expertise. I find onboard to be perfectly fine to my sound challenged ear. You will have to research the sound quality of the different chipsets used for sound.
One can always add a discrete sound card later.
If you are most comfortable with gigabyte, fine. But check out the others like Asus, Asrock etc.. too.
As far as I can tell, they are all good.