"So the best way to go would be get an o/r x-pipe or h-pipe? Then what?"
Not necessarily. As for that deep, muscle car sound I feel all Mustangs should have, after putting Magnaflow glasspacks (Magnapacks) on my car with the stock h-pipe, I was more than satisfied. Gave it a low, deep rumble in the lower gears and a muscle car "bark" when getting on the highway. That being said, I had two of my 4 cats removed by my exhaust shop and replaced with straight pipes and the sound when putting pedal to the metal is a lot raspier now than before. My car is a muscle car in 1st and 2nd but when accelerating now it sounds like a stock car. If you really want that muscle car sound, I would go glasspacks and an off road h, or see how much you like the packs on your stock h.
NOW: 1994 Mustang GT convertible, Forest Green, 60k ORIGINAL MILES! Flowmaster Super 40s and a Spectre CAI Filter Only.
THEN: 2003 Mustang GT "Black Betty"- Daily driver
K&N CAI, Magnapacks, Rear cats deleted, and all the potential in the world