What componant degrades the signal least/most?

There have been many threads on this website over the last several years which addressed the effects of different cables on the sound of a system.

In my mind virtually every other componant was a greater effect on, or adds it's own signature to the signal more than cable does. Every componant has connections (every connection is a loss of signal) resistors, capacitors, power supplies, boards. These things will effect an input signal more than a pair of terminations and a length of wire.

We all know that CDs and LPs are capable of sounding amazing. In the best systems they can be truly breath-taking. Most of us do not experience this at home though.

Where was that beautiful music lost? What componant contributed most to the loss of that signal?