The Kensei goes a long way to make sure every headphone or IEM you plug up is treated well with their IEMatch switch, which reduces output for high-sensitivity IEMs like the Campfire Audio Mammoths I played with, and their Turbo Mode, which does the opposite and increases gain by 6dB to drive power hungry headphones like the HiFiMan Planar magnetics I used. Regarding volume level output, you can control source audio from the Kensei in sync with the source device or bypass the source device’s audio controls altogether. The IE900 isn’t a bass-heavy IEM, but its 7mm dynamic drivers can energetically play back deep, dark bass via PEQ or digital filter tuning, as was the case with iFi’s XBass filter activated.