I have a G430 and I like it. The audio and mic is good. And your audio card shouldn't be affecting anything unless you're using headphones with 3.5mm jacks. Headsets with USB adapters have a built in sound card in them.
Initially, the G430 will feel a little irritating, you have to get used to it. The foam ear-cups will feel a little like you got a haircut and there's hair all over you and it's poking you.
It's really up to personal preference.
CSGO doesn't support 7.1, so you would need to use the regular "Headphones" option. 5.1 would sound weird.