This is true. I think his biggest problem will be with the Power FC.
My advice consist's of the following, seeing i owned a 4 door r33 auto at one stage.
1) Post in the WTB section of the SAU forums and let people know you need an R33 Series 2, Auto ECU.
2) Disconnect car battery and remove the Power FC ECU and hand controller (if it has one) and replace with your second hand r33 S2 Auto ECU.
3) If you already have a boost controller, i'd piss it off pretty quick and reconnect your boost lines into the stock boost solenoid to ensure either of the two items above arent causing the problem.
4) If the problem is still there and your running a stock ecu and boost solenoid, i would then locate another wastegate actuator and replace your current one. If your actuator is allowing your gate to open quickly, your turbo will spool around 8-12psi in an instant shot and give you a massive amount of boost spike.
However, you mentioned you had issues at 5,500rpm (Wastegate not opening soon enough), and now it spools to early (Power FC problem, Wastegate opening to early...Way to early...)
I'd seriously give the above a fair go.
Good luck.
Chris