You can choose between 3 mixer optionsFrom Volumio you can select the best mixer preference according to your audio chain.
First:
Go to SETTINGS menu
Go to PLAYBACK OPTIONS menu
Here, you have 3 mixer choices:
Software: mixer algorithm is demanded to Volumio OS
Hardware: mixer algorithm is demanded to the streamer board (suggested if you are using Volumio Primo without external DAC)
None: mixer algorithm is demanded to an external DAC/AMP