I just viewed answers to your question listed on this site under: Adjust Bass Level? .
I have a 2015 Mac Mini El Capitan, and listen mostly using Google Play. The post I mentioned has lots of folks needing answers, and there are A FEW. For one, when listening with iTunes, there IS a sophisticated soundboard for adjusting a range of 10 different frequencies. When on iTunes, go to the menu bar top-screen and click on Window, then Equalizer. That tool may get me to try iTunes, but I enjoy Google Play as my history of listenings there helps that site recommend music for me to hear.