I have to admit my equal length shorties and offroad h setup definately sounded a bit deeper at idle and cruise, but the longtubes and prochamber definately make more power and sound pretty scary under heavy throttle. I would just keep the prochamber, you may lose some power going with an h pipe.
Power means nothing to me when coming from the exhaust. If I need to rely on horsepower from my exhaust setup then my car needs some serious help. I'm just looking for a louder sound and changing my mufflers is without a doubt not an option. It's the mid pipe thats gonna be changed.