The last error with /dev/snd/controlC0 is expected. You should not attempt to manipulate /dev/snd/ nodes directly; that's alsa-lib's purpose/functionality.
Can you try an strace of LANG=C alsamixer, please?
The last error with /dev/snd/controlC0 is expected. You should not attempt to manipulate /dev/snd/ nodes directly; that's alsa-lib's purpose/ functionality.
Can you try an strace of LANG=C alsamixer, please?