I just installed the JBA and it actually sounds pretty good. Just a tad loud in the lower RPM but then I think it does tend to get ricey north of 4k. When accelerating normally, the floor vibrates and I know that nothing is touching the body or frame. It's just from the sound. It has that throaty sound that I love but that disappears over 4k. I'll try and get some sound clips and post them up.
Just one thing though, this kit, as-is, does not fit the EXT. All they would need to do is make a longer front pipe. What I did to make it fit was use clamps like these
Dynomax 35978 Dynomax Strap Band Clamps . The JBA kit came with normal u-clamps. If I would have mounted it as instructed, I would have been missing about 3-4 inches. What I did was basically connected the muffler using the band clamps with about 1/4 inch gap between the pipes and the muffler with the band closing that gap. By not inserting the pipes into the muffler, I gained that 3 inches I was missing. The rest fits just as in the shorties except that the front hanger does not line up (the first pipe after the cat) so I just turned that hanger pin around towards the tranny as it was contacting the frame. No big deal as it is already well supported by the cat pipe double hanger but I will probably look for something to support it eventually. And by using these clamps, I made this system completely removable. I could even replace the muffler with a Magnaflow if I wanted to try that. I did use the u-clamp on the resonator because it also has a hanger welded to it for the rear.
Stay tuned...