First off: the stock MAP sensor is capable of reading up to about 12 psi, which is already a lot more boost than the GReddy kit will put out without adding a boost controller. The limiting factor in dealing with boost is the ECU itself, not the MAP sensor.

When you get your car tuned on a dyno basically what they do is stick a wideband oxygen sensor up your tailpipe which gives a readout of the air/fuel ratios in relation to RPM. They then use whatever tuning device you have installed (S-AFC, Hondata, AEM EMS, Haltech, MoTeC, etc...) to adjust things like fuel injector duty cycle to get your a/f ratio nice and evened out across the rev range.

The GReddy bolt-on kit includes a "black box" that messes around with your stock ECU to get enough fuel into the motor. There's not really a provision for any further tuning of the a/f ratios. It's more a sort of bolt-on-and-forget-it proposition than anything else. That said, it won't run that bad without tuning since GReddy has done most of the work for you.

If you want to do it "right," you'll need a turbo kit that includes an intercooler, higher flow-rate fuel injectors, perhaps an upgraded fuel pump, and at the very least an S-AFC to tune it all. But that's significantly more of an investment than just buying the GReddy kit.

Pretty much it comes down to how much money you want to spend and how much power you're trying to make.