So i have Headset SteelSeries Siberia V2 Frost Blue and my motherboard is Asrock Fatal1ty Z97 Killer which have " Purity Sound 2 " Feature , but i'm confused if Realtek HD Audio Driver can improve sound perfomance/quality in my headset or not ?
You should already have the sound driver installed for your motherboard. If it's working, do not just install the Realtek driver unless you got it from the motherboard support site.