The line above the alternator that is cut looks to be the vacuum line that goes to the OEM boost control solenoid. I would go to a Subaru dealer or Ebay and get the oem vacuum lines and hook it back up like it was stock just to be on the safe side. Also you said that you are only reading around 5psi but the car still runs good? The stock boost is around 12psi so I am kinda curious if the gauge is working at all. Is the boost gauge swinging up and down with throttle input or just staying steady no matter what you are doing?