Just so you realize that the CEL could be because he has the boost controller solenoid unplugged since he has a MBC. If that code is not disabled in the ECU, then you will get a code for it. 6-7 psi is waste gate pressure. This does not necessarily mean the turbo is shot/bad it means that you have a boost leak post MAF. A bad turbo usually consumes an absorbent amount of oil (because it burns it when the seals go bad), sounds like a dentist's drill, or you get no boost at all. You can easily check for shaft play on the turbine wheel, you shouldn't have much in/out movement. Side to side is fairly common.
What else is done to the vehicle? IMHO, I would ditch the AEM Tru Boost and get something that is actually plug n' play (GrimmSpeed for example). Replacing a stock turbo with another stock turbo will not do anything negative or affect the ECU. Technically, a turbo upgrade wouldn't even affect the ECU if you are running the same amount of boost/fuel. You need the tune to actually take advantage of the mods and up the fuel, timing, boost, etc.
2007 WRX TR | Stage 2 | PAR Gearset (Built by AndrewTech)