Running a H Pipe,whats the advantage

I just bought a set of headers from TTI saturday, and talked to "Sam" who is the engineer of the TTI headers. We talked about a exhaust system for my car also, and I decided to connect a three inch system to my new headers, and I popped the question about the "H" pipe and the "X" pipe. Sam said they both increase HP, - around 10hp for the "H" pipe, and 17-20 hp for the "X" pipe. ALSO, they both give you a deeper throatier sound...