resolving source + muddy amp = audio that is less detailed
resolving source + transparent amp = audio that sounds realistic
resolving source + transparent amp + resolving transducer (s)= audio nirvana
In terms of importance, it goes like this:
1) Transducer(s) (headphones or speakers)
2) Amplifier (solid-state or tube)
3) Source component (DAC, CD player, record player etc.)
Because the headphones or speakers is the final point of contact beween you the total sum of your system, how resolving they are will greatly influence what you hear.
A bad amplifier (that is not audibly transparent or a wire-with-gain, in other words colored-sounding), will limit the full potential of your source component(s) and headphones/speakers.
You could have an incredibly detailed DAC, CD player etc. that provides the true analog-sound (like real life) sound of digital, or even top-notch vinyl. But if the sum of all parts are not aligned, it will be like looking at a beautfiul sight through a foggy window (in terms of what your ears are able to discern and appreciate).