Well, not really an "exhaust" but enhancing the factory "fake" system, the BMW Active Sound.
The kit contanins everything you need: Maserati ECU sound, BMW I8 bluetooth interface, BMW i8 specific cables, install manual.
You can control everything from your phone app, you can set it as loud as you want, quiet as a mouse or everything in between. The app links to your car profiles Confort, Eco and Sport and you can assign volumes, tones and even start exhaust sounds to each one.
We did two cars today, it's absolutly incredible and you do not void the warranty, everything is reversible, it takes around 2 hours for the install.
Here is a sample of the sound, with sound booster / factory / with sound booster again.
http://vocaroo.com/i/s1KStw0jkLQo