I just installed jba's (lt's) and the h pipe (off road) with flowmaster's and it still sounds very raspy, i am going to put stock mufflers back on, from what i have researched they seem to sound the best with that setup.
I have a offroad h and it sounds good, i had a offroad x and it was terrible very raspy like you are explaining. I think the long tubes will make the tone deeper, it's worth a shot.