I thought that if you put a dual muffler setup on a 4 cyl., then you would lose power?

I am reading all this stuff about people putting the SVT exhaust on their zetecs and loving it. How big is the exhaust pipes on the SVTs? I already have one magnaflow muffler on my car, but wanted duals. I also have the resonator removed, but still have the stock pipes to the back. Not sure how big the pipes are. But i have been looking into getting bigger pipes, just not knowing what to get. So if i order an SVT exhaust, could i buy another magnaflow muffler, and put them on the SVT Exhaust and it sound good and still keep the power, or gain power????

Thanks for the help and sorry for all the jibberish.
Tony