Mxplayerは単体で使うものではないんやで
Mxplayer + Poweramp Equalizer

Poweramp Equalizer　神アプリ
https://play.google.com/store/apps/details?id=com.maxmpz.equalizer

yutubemusicもamazonmusicも格段に高音質化

adbコマンド
adb shell pm grant com.maxmpz.equalizer android.permission.DUMP