I think to some degree hearing can be like smelling or tasting. You have to have a palate cleanser. It's like smelling a hundred different flowers and trying to pick out the subtleties. At first, you can point out all the different tones and timbres, but after a while it becomes confusing and they all sort of smell the same. Then you smell something else, like coffee grounds, and voila!! You can smell the details again. With sounds it's a similar thing. When you can't hear the differences you might need a break, listen to some harpsichord and lute music, and then come back later with fresh ears.