I managed to make it work on zenfone 2, but i noticed something very wrong with viper4android.
The more push volume effects like compressor, playback gain control or Master limiter, the more the android native volume control becomes ineffective.
This is easilly explained by the fact that maybe viperfx sits "after" the android music volume control, see the following example, this is happening to me:
Played Music (-30dB) -> Android volume control (-80dB) -> ViperFX Auto gain control (0dB) -> speaker/headset (0dB)
In that case, even if i lowered the android volume control to the minimum possible (one step after zero), viperFX comes to play after it, raising the sound to 0dB again.
To support my thesis, i can hear a lot of digital noise, probably due to the fact that ViperFX is doing an insane work raising a very low volume to 0dB.
Indeed, using the volume slider, does not alter the volume anymore, but just eliminates the digital noise as i move the volume slider up.
Everyone can test it.
Play some music
activate playback gain control, push it to extreme, set max gain to infinite and max output to 0dB.
now slide the android music volume to the minumum (after zero) and hear that the music does not lower the volume; it just becomes more noisy.
The final question is: is there a way to make viperfx operate *BEFORE* android volume control?
Please ignore, rebooted, and it works as it should (wth?)