Pisound does not have hardware volume controls that can be used with ALSA, it plays the raw data that it gets from the OS.
It is possible to add a software ALSA plugin for controlling the volume however, see here:
https://alsa.opensrc.org/How_to_use_softvol_to_control_the_master_volume
The best solution however would be to deal with too high volumes in the software that is producing the audio by reducing its output volume, if available.
Btw, some users had distortion issues because of the power supply they were using. Our recommendation is to use this one.