Well, you are basically trying to compare the difference of a middle-of-the-road amp and a top-of-the-line amp. You will see that the power-supplies are different, and their ability to play loud for long periods of time. It's like comparing a new Mustang with the V6 in it to the Mustang Cobra...same but very different.
Are there some die-hard Rockford guys that can explain this better, I am not totally up-to-date on the Rockford stuff...