While every Ferrari is designed to be rung out on a race track, the 599XX basically needs to live on one. This extreme supercar isn't street-legal and is only available to a few select Ferrari owners with lots of liquid assets.
Major upgrades over a standard Ferrari 599 include:
Aerodynamics - In addition to the usual wings and diffusers attached to the cars, this Ferrari has active aerodynamic aids (also known as fans) to extract air from under the car and provide even more downforce as needed.
Power - A host of lighter components, new intake and exhaust parts, and internal modifications to the V-12 engine allow it to spin up to 9,000 rpm and produce a maximum of 700 hp.
Transmission - A new shift map allows gear changes to take place in a mere 60 milliseconds.
Brakes - All the other go-fast upgrades wouldn't do much good without better brakes, so Ferrari chose carbon-ceramic brakes and fitted F1-inspired doughnuts to help keep the brakes cool.
Anyone fortunate enough to be asked to purchase a 599XX is pretty much subject to the same rules as the FXX owners, and quite likely took delivery of an FXX in the past. This means the 599XX can only be used at Ferrari-organized track days and other Ferrari-sanctioned events. Don't expect these cars to be appearing on eBay Motors anytime soon, either. Ferrari will probably want to make sure all 599XXes end up in loving homes where they can be flogged on the track instead of resold for an enormous profit.