MAX98357a not working

I use the max98357a in stereo. So, one is for the left and the other for the right.
I configure it in the standard RPi configuration, with


in config.txt file. (the sdmode-pin=16, makes that it is muted and does not pop at all)

Now the question, how to get it working with Volumio?
I tried to select max98357, however, than the sdmode pin is keep it muted.
Modifying the config.txt file gives an Alsa error.
Can you give some guidance?
Many thanks,