Equalizer and Beats audio

More than one equalizer is a bad idea.

Beats is nothing but an equalizer. (one that is pre-set).

If you go to Settings, / Sound, Sound Enhancer, you can choose to use Beats or any one of about 8 other equalizer profiles.

One of these is No Effect.
If you have an equalizer that you want to use, you should probably choose No Effect, and then use the equalizer.

(On my international version, no equalizer came with the phone, although I could install one from the market if I wanted. I just don't see the need.)

To match beats to a specific headset, choose Beats on the screen mentioned above, then there is a pull-down at the top that allows you to choose which type of headset you are using. (And you can choose any of the three regardless of which actual headset you have). I set mine to Solo even thought I don't have Beats Solo, because it sounds a bit brighter to my tin ears.