I think one of the hidden factors in our quest to enjoy our high-end audio systems is how hard our brains work at processing the sound we hear - less processing equals less listener fatigue.
Good friend and fellow Audiophile Mark Lewis wrote me a inspiring note that suggested he enjoyed his time in Music Room One with the IRS because he had less processing to do - everything more separated, clearer - the illusion of soundstage so real your senses had less to fill in and imagine.
We're all familiar with the phenomena of Listener Fatigue - when something we hear is too bright or harsh, too loud, too complex - our brains have to either guard against or untangle the sound fields we hear and this is work! The harder we work the less we relax and enjoy what we hear, the more fatigued we get.
Surely one of the very best indicators that you have everything in your system dialed in right is the feeling of wanting more after a listening session. I can't tell you the number of times I have listened to a new DAC or amplifier - found myself enamored with its sound - yet felt fatigued after spending time with the device or thrilled to put the next track on and can't get enough of the experience.
Certainly some of this can be mood, but overall if you find yourself wanting more, you've got something quite right.