Anyway, back to the topic, the explanation in the Apex USA site explains everything although not in a very clear form, maybe a little hard to understand.

 

and have a look at this:
http://www.motec.com.au/m800.htm

 

Sorry, explaining these things to you is too much for me, try your girlfriend, she can explain things to little kids, can't she??

 

I imagine that when the EVO comes to the U.S AEM will have a standalone ECU to support it. I have heard some cool things about there new standalone ECU's they can do just about anything you can think of and more and you program it yourself from your laptop.