I just purchased a new A5.5 which I find to have a more tube like sound that my A5 I had a while back ago. I also found that the volume knob seems more linear as it is smoother when I use the remote and doesn't jump around as much. The only thing I found out, is I get little or no sound about a quarter of a turn, and start getting music at about half way to the half way point. Seems odd but, is this the way they redid the Amp, as I know it went through some more refinements which I like, especially on the sound. The A5 was fantastic, the A5.5 is more smooth and tube like. Thanks .....