I have noticed while listening through headphones that after a certain amount of time the sound seems to improve in a listening session. The soundscape expands, a more of a rounded and real quality to the music. Time was I would say the components were warming up. I suspect this is just somehow my auditory system needing time to adjust or get acclimatized. I wonder what would be going on physiologically. Closing eyes has an effect as well. I believe in this case the visual system is dominant and shutting it down accesses more brain power to the ears.