Air filter questions ?

Hi, i just bought my first Mustang GT, a 2001 in Laser red. It is awesome and i was wondering about upgrades. i want to change the exhaust for a 2 1/2" cat back MAC system so that it sounds as good as it looks. I have read a lot about these cold air kits and general opinions seem to be that they are not worth the money. I think that K&N do a filter that mounts inside the original air box and a kit that does without the housing, like their filter charger kits for other fuel injected cars. Does anyone know if that is correct ? Also do you get the induction roar so common with K&N's on this motor. This car is awesome, just awesome.