Well, I'll go ahead and explain why CAI aren't good for the WRX. The bend just before the mass airflow sensor disrupts normal readings. What actually happens is it creates turbulence which essentially circles around the area of the MAF. This throws the reading off and has a habit of leaning out the A/F ratio in our engines. The best advice is to not install it. Otherwise, WRXKidd775 was nice enough to give you instructions.
"We live for a good time, not a long time."
RIP Colin McRae