What are the bennifits for having a Hpipe or a Xpipe instead of strait true dual? Does it effect sound and power?

 

The cross over tubes in an H or X pipe helps in scavenging for the exhaust system. Tone will change pending each system, and "typically" an H pipe will produce lower end torque and a deeper tone, while an X pipe will help in higher RPM horsepower and a raspier sound. But, sound will also depend on muffler type

 

Havng an H pipe or and x pipe
lets the exhaust scavenge from the opposite side as the exhaust gasses are pushed out of the cylinder .

The scavenging that you get from the x or h crossover helps to pull more burnt exhaust out of the cylinder as it pushes exhaust gasses out. With out this scavenging effect more burnt exhaust gas remains in the cylinder leaving less room for clean o2 rich mixture .
It defiantly helps to increase flow and picks up some torque and power at the same time.