There is a  dffference between controls setup in HAL and Softmixer.
HAL Controls are adding dbscale, which should not be the case if not specified.

Example specified:

 "halmap": [
{
"uid": "agl-master-playback-volume",
"info": "Sets master playback volume",
"alsa": {
"name": "Master Playback Volume",
"value": 95,
"create":

{ "type": "INTEGER", "count": 1, "minval": 0, "maxval": 100, "step": 1 }

},
"action": "plugin://hal-unicens#MasterVol"
},

 

*****

Checking values for UNICENS HAL
~> amixer -Dhw:ep016ch cget numid=1
numid=1,iface=MIXER,name='Master Playback Volume'
; type=INTEGER,access=rw--RW,values=1,min=0,max=100,step=1
: values=4
| dBlinear-min=-100.00dB,max=0.00dB

The Value can be set by cset but alsamixer is not matching correctly.
~> amixer -Dhw:ep016ch cset numid=1 40
numid=1,iface=MIXER,name='Master Playback Volume'
; type=INTEGER,access=rw--RW,values=1,min=0,max=100,step=1
: values=40
 dBlinear-min=-100.00dB,max=0.00dB

****

In Comparison, the softmixer controls are added correctly. No dbscale.
~> amixer -Dhw:2 cget numid=1
numid=1,iface=PCM,name='PCM Rate Shift 100000'
; type=INTEGER,access=rw------,values=1,min=80000,max=120000,step=1
: values=100000