An air filter will sit inside the existing box, an induction kit usually replaces the box with something else.
A simple way to deal with the 899 is to obtain a cone filter that will mount directly in place of your filter box.
Exhausts are a different problem, you can up the size of the exhaust, that certainly makes it sound louder and, according to those that have them majes the car feel qicker. The manifold is, however, quite restrictive in its design so I have a suspicion that the extra noise just makes the car seem faster.
Cheers
D