Another option for people who want Dolby Atmos, and more importantly DTS:X and Auro 3D, Smyth Research is getting very close to releasing their updated VSS system, the A-16. You can still preorder at a discounted price until the end of September (price is expected to jump up ~$500 to it's regular selling price of ~$2295).
You can currently order it for $1795. If you don't have the space, money, apartment, etc. for a full blown 7.2.4 (this may be expanded up to a maximum of 16 speakers), this is probably by far the greatest way to experience 3D audio through headphones. Check their kickstarter page, or the thread running on head-fi. It will take measurements of your ears, has head tracking, a "store" where people can trade and buy different surround systems from around the world (like Radio City Music Hall or any other theater that people record the appropriate files). Since some people may have to pay to get accesss
Have a friend with a $20,000 7.2.4 system? Take your A16 and record the room, and the A16 will sound 99% the same through your headphones. The A16 will adjust your headphones to replicate the sound as closely as possible (So obviously better headphones will probably do a better job). They used the Sennheiser HD800 for development, and the HD650 works well too. People who have had the demo had jaw dropping moments. The demo puts you in a 7.2.4 surround sound room. Speakers play when the headphones are off your head. Put the headphones on, the speakers drop out and the A16 takes over. Hundreds of people cannot tell the difference between the speakers playing and the headphones!
You have much more control over the entire experience, and you aren't limited to Atmos. It takes the audio out from HDMI and does it's magic. It has 4 HDMI inputs that are 2.0b and HDCP 2.2 compliant, with one HDMI out. The A16 can be bypassed (pass-through) so your surround system can still be used. Just plug the A16 into your AVR.
I have been gaming with virtual surround sound for 7 years now. While my current Creative SoundBlaster X7 (SBX VSS) does a really good job with 5.1 or 7.1 feeds, it isn't even close to what the A16 does. For me this is the far cheaper option to get into 3D audio, and really there is no way for me to even attempt a full 7.2.4 system in my Philly apartment.
I really hope Microsoft and Dolby can fix this headphone app. $15 is nothing if it actually works when they fix the kinks. The Smyth Research system is another world, where you can change just about everything. Their A8 was very successful and twice the price (without 3D audio).
Figured I would drop this in here as some of us AVS members are a little insane and want the best possible sound. I can't fathom the A16 being topped for a long time, and the pre-order discount is running out fast. I went with the A16 2U, which is the rack mount version. They also have a headphone stand type that is pretty unique. They recently posted pictures of the production models. Check out their Kickstarter page which explains all of this FAR better than I can.