I went through the exact same trouble shooting steps and have the same problem as the other user who posted this problem.
My sound fizzled out on my R speaker. As I turned it up louder, it would kick on fo a while, but now no sound. The speaker itself is not the problem because it works when I switch it to the left channel fine. It's not the dock cable either. I think it's the amp itself.
Please advise.
PAC