the problem with the maual boost control on your set up is that , you never know how much your car is going to react to the slightest adjustment of the boost controller. you might turn it a 1/4 turn and get a 3 psi reaction. if that happens , say goodbye to your engine.
I say , if you have a maf sensor in a subaru , don't mess with manual boost controllers unless you are a tuner , have a tuner that checks your tune after every fill up, or have a lot of cash to repair your car.
Besides, just turning up the boost on your car with those mods will probably make you slower, the ecu will compensate by retarding the timing.