Can you give us your take on the sonic differences between the 550a and 560? Not necessarily the differences in frequencies but in harmonic content, saturation and the like.
I have 2 550a and am interested in the 560.
I use and like both. I couldn't tell you, technically, the harmonic and saturation differences. You can get what you want from each of them but with different and equally satisfying results. Experimenting with it and listening to what it does is the best way to judge.