Realtek codecs generally don't have anything like CMSS-3D Headphone or Dolby Headphone to my knowledge, barring some motherboards that come bundled with a Dolby Home Theater or X-Fi MB software package.
I'd still advise picking up a used X-Fi (non-XtremeAudio, those are fakes) or Xonar DG (if you can't get a true X-Fi card for a reasonable price in your area) if you have an expansion slot free. Shouldn't cost any more than US$40 shipped.
The AD700s are very easy to drive, so no worries about amplification, even with integrated motherboard audio. I'd be more concerned about a clean analog audio output (no buzzing or hissing whenever you move the mouse or have any drive activity going) and gaming audio features.