Thanks! Fixing the amixer path in line 252 allows alsa to be up and running on boot. The command "amixer" in line 173 shouldn't cause issue as /usr/local/bin is in our $PATH, but the /usr/bin/amixer in 252 is a problem.
I still don't have mixer settings persisting across reboots but at least alsa can be autostarted. I will update the alsa_modules extension with the fix which will be good enough for now. When I have time I will get mixer settings to survive a reboot.