Power Commanders suck these days. There's virtually no point in them with the ECU reflash capability these days. Not many people have them, so not many people will be selling them.
The little thingy under your seat doesn't twist to activate the cat. The cat is always there unless it's sleepy. The little twisty thingy pushes and pulls the metal stringy thingies to move the valve in the exhaust so the cat isn't so loud when it purrs.
The flapper thingy in the rushing air hole is to help with the cat burps. There's one flapper thingy in there. Did he remove the flapper plate thingy or do some shir with the electrical whisker thingies that hook to it?
Some other thingies you might need to know...
*Catalytic Converter
*Exhaust Servo
*Exhaust Servo Valve
*Ram Air
*Air Intake Duct
*Fuel map
*Ignition map
Your fuel map is closed-loop if it's equipped with an oxygen sensor. Only the Euro versions are. Otherwise it runs open-loop. The oxygen sensor thingy is in the catalytic converter. If you hook a Power Commander to that setup without disabling the oxygen sensor, then it do anything since the computer will try to fight the Power Commander. You have to disable the oxygen sensor. If it runs closed-loop, then your fuel map will compensate and try to go back to the factory settings in it.