aftermarket management would be the way to go and possibly a boost controller, then before u start playing with bigger turbos, have to consider, upgrading fuel system, and rebuild engine with stronger internals so it can cope with the power level and higher boost levels that bigger turbos produce
if you don't want a full on ecu, get an apexi safc or safc II which is a piggy back air fuel controller, i just got mine unitl i can afford a full on ecu
adrian