induction kit

hi, i have been looking everywhere for an induction kit. at the moment i have a bmc replacement filter, but i want to get myself something like the p' cross viper, green twist, k 'n' n apollo or the bmc CDA. i emailed a company and they say they do a bmc cda one for my car but im not too sure as its not a simple slip on jobby, it has to be screwed in? does anyone know anything bout them. by the way i have the a3 2.0fsi non turbo 2003 8p!!!

cheers guys!