Some information for you all.
A wastegate is a diaphragm that opens a valve. That's all. The MSP one is set to open at around 7 psi. It's triggered by a signal line - a hose that's connected to the turbo output. The pressure pushes on the diaphragm and opens the wastegate, dumping exhaust gas. On some wastegate designs, it's possible to change the springs to change the boost setting.
A boost controller takes that signal line and bleeds off some of the air. This means that the wastegate will still open when it gets 7 psi of pressure, but the turbo might be producing 12 psi at this point and the controller is dumping 5 psi. Make sense? The closer your mechanical boost (set by the wastegate) and your boost target (from the controller), the easier it will be to control boost.
Notice that I haven't mentioned manual or electronic boost controllers, or integral or external wastegates. Makes NO difference. An integral wastegate can allow you to run massive amounts of boost if everything is set up correctly. Electronic boost controllers allow you to spool up more quickly because of the way they spill off the extra pressure, but that's it.
No boost control can give you lower boost than your mechanical setting.
The stock ECU has a fuel cut at 10 psi to stop you from blowing up your motor by installing a simple fishtank bleeder and raising the boost. The ECU does NOT use a MAP sensor, so Grand National parts will do you no good at all.
A turbo with a T3 compressor housing and a T25 turbine housing is a T28.
Keith