How to adjust HifiBerry mixer settings in Rasplex

Whenever I’m playing mp3 files I experience clipping and I need to reduce the Plex volume. It’s a bit fiddly trying to reduce the volume via my iphone and whilst searching the net I’ve found a potential solution on the HifiBerry website.

They recommend the following settings


 amixer sset 'PCM ' 96%
amixer sset ' Playback Boost ' 0%

Any idea how I would implement this in Rasplex?

https://www.hifiberry.com/guides/mixer-settings/