For 1080p though, why not save the cash for the next upgrade. Future proof is not about getting the fastest thing available but rather making sure your resources ie money or whatever you buy with them, will last their longest
Also OP, if you are so concerned about audio that you would drop the x99 and go for z97 for the onboard chip, then i would just get a soundcard, since even a cheapish one is miles better than onboard.
My thoughts exactly about the future proofing and saving money based on my user needs. I feel a lot better with the 970 at 1080p as it would leave money over to get peripherals like a mechanical keyboard mouse and headset or like you said put it away for a future upgrade.
About the sound, I have never used a sound card and am not too sure about headsets that have jack connection as I have always used usb stereo headsets.