My headset settings, I paired my O2X with IEM JVC FXT90. Most of my music is in lossless format, I use PowerAmp with AlsaMixer. I'm a basshead and my equalizer is flat. Other settings that are not mentioned here - I turn it off. I like my music loud with strong bass punch (not boomy), high a bit crisp, and vocal is forward along with the musical instruments. I used Viper4Android FX version 2.2.1.1. on TonyP's CM11 + Pengus latest kernel:
Playback Gain Control: On, effect: slight, max gain: 4x, max output 0 db
Convolver: On, impulse response: Urei 1178 impulse
Dynamic System: On, listening device: common earphone (v2), dynamic bass: 8%, tube simulator: off
Fidelity Control: viper bass: On, bass mode: natural bass, bass freq: 40 Hz, bass boost 3.5 dB, viper clarity: On, clarity mode: natural, clarity: 3.5 dB
Master Gate (Limiter): output gain: 3.5 dB, channel pan: 0.5 : 0.5, limit threshold: 0 dB