The VF39 is a popular choice due to availability. CobbTuning.com actually lists several VF39 maps which you could download and use for your car, but be extremely careful to follow the map notes exactly. Pay particular attention to the gas Octane (91 vs. 93) and download the map specific to what you have available in your area.
If you choose to download an off-the-shelf AP map, in addition to your AccessPORT, cat back, and Cobb SF intake, you'll also need:
- aftermarket downpipe (map notes call for one with a high flow catalytic converter)
- STi Pink 565 cc injectors
- an STi (or equivalent) TMIC
- and obviously a VF39 turbo
Personally, I would recommend getting a professional tune because you could also consider purchasing and installing additional parts such as a 3 port electronic boost control solenoid, larger fuel pump, and possibly some other parts which are commonly added at this point. Any off-the-shelf map will be on the conservative side since they're made to work for all cars and might leave a bit to be desired. Only a professional tuner will be able to tweak the settings of your specific car to safely maximize power which is what most people want.
* Note: You'll also want to invest in a catless up pipe and I'm not sure whether or not that will be compatible with the AP maps. Getting a catless up pipe is a safety mod for all pre-2006 WRXs since the stock up pipes have a catalytic converter. Modifications and age can cause bits of the catalytic converter to break apart and cause potentially expensive damage.
** Another note: Make sure all maintenance is up to date before modifying anything. See this link for factory recommended maintenance: http://www.cars101.com/subaru/subaru...000Maintenance