Newbie XF owner here, Newbie car guy too. My near showroom condition 36K-mile '05 6Sp NA Coupe is completely stock. I think it's pretty peppy, but I'd like to max out that pep while keeping it aesthetically as stock as possible. I would like to do a tune and throttle body upgrade, as these appear to be the most effective means of squeezing out a few additional horses.

Can someone explain what it is about the stock intake that renders it inferior to an aftermarket CAI?