hey, its nice to see yet another WRX being modded, i have a link for you that might be helpful for connecting speakers...
its the only one i could find, if the site goes down before you get it (for whatever reason) i have it saved on my computer as well.
good luck with your install, and although it is an '06, my '04 is very similar so if you have a problem maybe i can help ^^
good luck! (p.s. use the 12v accessory wire from the speaker heading for the iginition wire to the psu)