Search headers. From what I have read I dont like the headache and cost of them compared to what you would get out of them, even with an aftermarket turbo. PnP'd headers with a high flow crossover seem to do just as good and its not as expensive a set up.
As far as boost goes, if you have your AP if gives you boost, its a bling thing, nothing special, just something to watch I suppose. Most say its not even that necessary with a stg 2 setup. But thats a decision for you to truely make.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX