[rk3399-gru-sound] Alsa won't mute speakers

[apokalypz]

The wiki provides directions for rk3399 chipset devices based on the GRU board to get headphones working with alsa UCM, but it doesn't mute the built-in speakers when plugged in. In fact, I cannot find ANY alsa mixer controls that successfully control the speakers, just the headphones and various inputs. There is a switch labelled "Speakers", but toggling it does nothing. I read that people with the hifiberry pihat for raspberry pi that has the same audio codec as my speakers (MAX98357a) need to use a software volume control via the /etc/asound.conf file, but I intend to use pulseaudio so a custom asound.conf probably won't work for me right?

If anyone has info about this and can point me in the right direction, it would be very much appreciated, already wasted whole days on this simple but annoying issue.