The OEM guys have it easy, their calibration is meant to run a specific engine combination. It is much easier for them to implement adaptive strategies that automatically compensate for changing environmental or operational parameters. The DFI, Fast, and other aftermarket systems have to be flexible enough to handle whatever engine combinations are thrown at them. This makes the adaptive stuff a little trickier to handle, but it is there just the same. Mostly it just requires a little tuning to see how a particular combination will react to changes in operating conditions. Once this is known, the calibration tables can then be programmed, and your adaptive strategy starts working.
The DFI Gen 7 box in particular has many features that cause it to operate very much like the adaptive features of a stock pcm. As mentioned, the presence of an internal barometric pressure sensor allows automatic adjustments to be made to the fueling strategy while you are driving to compensate for changing weather or altitudes. The unit will also alter it's fueling strategy based on feedback from an exhaust gas oxygen sensor in order to attain a pre-programmed target air-to-fuel ratio. Idle strategy is handled differently for stick cars vs automatic trans cars. On-board self diagnostics will detect problems and generate an output on a MIL line, as well as set error codes that are visible in the calibration software. Many other trims and compensations exist, most of them are based on preprogrammed calibration tables that need to be set up for your specific engine combination.
Once the calibration tables are set up properly, your car will run every bit as good with the DFI module as it did with a stock PCM before any engine mods were performed. The main benefit to aftermarket systems is that you can adjust for any changes that are done to your engine. Unless you do it yourself or pay ALOT of $$$, most custom flashes or performance chips for stock pcms are not much more than educated guesses as to how your engine mods might affect the driveability of your vehicle. "Real" custom flashes, done by someone with access to OEM calibration software, are usually more expensive, and tend to be more effective. However, there is only so much that can be done with the stock pcm before you start throwing trouble codes or run out of adjustments that can be made. That is where the aftermarket systems really begin to shine.
