si lo tienes rooteado puedes intentar cambiar system/etc/huawei/audio/U9200_audio_config.conf, asi:
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[Music]
<speaker>
Handsfree Playback Volume = 27
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<headset>
Headset Playback Volume = 9
DL1 Media Playback Volume = 118
SDT DL Volume = 107
DL1 Equalizer = 3
y cambiar SDT DL Volume = 107 a SDT DL Volume = 120