I know their products well; The developer is a very nice guy and very helpful.
The basic MAFT is not a very tunable device. I don't know how much adjustment the potentiometers inside allow for. I can think of a couple tricks to squeeze a little more out of the stock injectors with it but it's not significant and not what the decive is built for. The ECU is calibrated for the amount of fuel that the stock injectors flow per a given unit of air. No matter how you tweak the system you will always be limited by the ECU's maximum allowable duty cycle for the injectors. So, either you need more fuel per cycle from the injectors so that when tuned for an ideal mixture the ECU will actually believe that less air is coming in than is the case or you use a FCD to lie to the ECU along with a fuel controller to tune the injectors closer to the edge of the ECU's fuel map per RPM.
There's no cheap cheat that's widely recommended... FCD's are old tech and very unpopular with the Supra crowd (for good reason), adjustable fuel pressure regulators are recommended for tuning purposes but seldom for an adjustment of +/-10% (especially not on old injectors).
Your friend's not thinking it through or thinks you've got some additional means of controlling your fueling. Physics and math: 25% more air needs 25% more fuel.... That right there negates the possibility of running the Lex AFM with the stock injectors. The popularity of the Lex AFM is it's simplicity (please people, stop trying to complicate it
): Add Lex AFM, swap injectors and GO DRIVE!!! No electronics, no tuning, no time on a dyno needed, you keep the protection of fuel cut but it's bumped up 25% along with the air and fuel.
The MAFT Gen II is a probably a better option which is thoroughly adjustable. Much of its functionality mirrors that of the MAFT Pro but it lacks the boost control and AFM/MAF deletion capabilities. It does support GM MAF conversions though. This does have fuel control capabilities and timing control. I believe it's also capable of capping the Ks freq output such as an FCD does.