Negra has a sound clip on youtube:
YouTube - Tundra5.7 Powerstick1 .
From what i heard and x or h pipe doesn't effect the torque or hp. It only effects the sound of the exhaust. The x pipe tends to be more raspy and a little louder than the h pipe. The h pipe adds that deep tone to your exhaust or "bass" as some say it. Does anyone know the size of the stock piping? And when you get a supercharger does the piping size change?