By all accounts the difference is in the quality of the sound, although I have not heard the two side by side. As I recall the G-56 sound is described as mellower and deeper.
As the stock exhausts were already punishing my ears I went with G-56 and am very happy. I think in general they are quieter, But they are not cheap!
I am use to sound. I have a chopper with short straight exhaust and have ridden Harleys for years so sound doesn't bother me. Frankly I feel that the stock exhaust is a little quiet for the big v twin sitting up front. I am really looking for comparison of performance. The engine is really restricted and I was hoping to find out if the baffle removal performed as well as the G-56. I am thinking about removing the cats next.
Oh and you are right about the price. Over $2000 USD shipped. There will have to be a huge improvement to justify the cost