The tube amps are the best for signal reproduction, Semiconductors are too 'fast'. When a signal change is passed through a tube, the change is 'slower', the change from one note to another is smoothed. With a semiconductor, each change is immediate, due to their speed of response.
The 'smoothness' is where the analog signal shines.
With digital sampling, even with Nyquists' Theorem, you still have that 'choppiness' due to the 'speed' of the semiconductors. Then you get into compression, or "Music with holes in it". The compression takes away something from the original, by its' inherent nature, so you have missing parts. I guess that's why the kids play such obvious crap at painful volumes, to cover up the missing pieces. It's been sampled and compressed so many times that it bears only scant relation to the original material.
Then there's the issue of synthesizers.
I remember taking in the Marantz amp for repair and having the guy who tried to pick it up almost hurt himself because of the unexpected weight. His remark was that he "forgot that they used to put stuff inside those boxes".
