warranty depends on whether the modification has played a part in damaging the part.
ie, if you have an exhaust and your diff goes, your warranty should be fine.
so if you were to blow a motor and your car had a cai, subaru would be given enough rope to void your warranty since its altering the system that they have sold you.
do more research before you put on a cai onto a my06. later model wrxs/sti's dont take too kindly to modifications to the original system due to the
ecu's configuration.