go get yourself an injen CAI, very reputable, easy to install, SELF TUNING, and about $260 on killertc.com. as for an exhaust...well you have tons of options, personally i have an injen SES catback exhaust working with my injen intake, beautiful combination. as for axle back and cat back, a cat back exhaust replaces the exhaust from the catalytic converter all the way to the back of the car. An axle back exhaust replaces the exhaust from the axle to the back of the car. so if you just want a sound change and some better airflow with mild horsepower gains, go for the axle back. remember, it's not easy but you can go back and get the rest of the piping later on if you decide to eventually replace the stock header and remove one of the catalytic converters. you have two, just so you know
greddy makes a great exhaust, look into the EVO2, also Agency Power has a new one for the tC, go to youtube and search for the brand of the exhaust along with your tC to hear an idea of what each will sound like.