$ amixer
Simple mixer control 'Master',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 65536
  Mono:
  Front Left: Playback 65536 [100%] [on]
  Front Right: Playback 65536 [100%] [on]
Simple mixer control 'Capture',0
  Capabilities: cvolume cswitch cswitch-joined
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 65536
  Front Left: Capture 65536 [100%] [on]
  Front Right: Capture 65536 [100%] [on]

I don't get all the same information that you do from alsamixer.  I also noticed that my value ranges are drastically different.  My Simple mixer control looks like your Output Mixer Hifi.  Why wouldn't mine show the same fields of information?

BTW, I want to get this to work with "Crankshaft" which is actually raspbian stretch but with the free forked version of "Open Auto" but you probably know that already.  The developer of that build put in support for the AudioInjector Stereo/Zero cards and at least one user confirmed it working.  It's just got to be something weird with mine.  I didn't add anything extra.  Although earlier today I added a file called /etc/asound.conf which is supposed to set the specified card to default.