So we have setup a JustBoom DAC with a rotary encoder on GPIO 23,24.
Followed the steps in our guide till the end of section 2 to configure the OS.
and the extra steps from M2P
https://www.max2play.com/en/2016/12/rotary-encoder-ist-now-compatible-with-justboom-sound-cards/
and all works fine for us.
If you have a keyboard/mouse and a monitor or can access via SSH, you could run the alsamixer to verify that indeed the volume slider works with the rotary encoder.
I hope this helps.
