After thorough testing, I went through ALL the options that are related to volume, subwoofer or amplifier settings of the device. None of them made any impact, not even to the weird 87% value. After going through every option in Poweramp, related to volume, DVC, OpenSL, resmpling, etc.. still no impact. It keeps resetting on either a constant interval or upon changing the volume manually, i.e. through the volume buttons.