lots of good comments about effortlessness already.
the word that comes to mind for me is ’headroom’; effortlessness in music reproduction requires all pieces of your system puzzle to operate in their best region of efficiency. if a piece in the chain is being stressed that causes distortion and inhibits the free flowing ease and authority which equals effortlessness.
another aspect of effortlessness is bottom octave extension past the needs of any musical material. this margin of error allows the music to matter of factly do deep bass without strain. having 10hz-20hz system performance requires extension below that.
effortlessness also comes from power grid optimization and anti-resonance treatments which allow the musical focus to hold together as it scales and not get muddled by strains on A/C power or hash and distortion from high SPL resonance feedback.
i could go on and on.
effortlessness has been a central theme of my system evolution. take a look at details of my system to see what i mean by that.