Mopidy Discourse

How to configure alsamixer for optical output?

Hi, I have Mopidy 3.2.0 on Ubuntu 21.10 and I want to use an optical output with adjustable volume using Mopidy-ALSAMixer. By using only the configuration below I get optical with adjustable volume (tested with e.g. Iris and Mopidy Mobile):

[audio]
output = alsasink device=iec958:CARD=PCH,DEV=0

But when I also use:

[alsamixer]
# same for IEC958
control = Digital

the volume is not adjustable.

Please help me with the correct setup,

Thank you!

Below I list the output of aplay -L and amixer scontrols.

$aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
default
    Playback/recording through the PulseAudio sound server
samplerate
    Rate Converter Plugin Using Samplerate Library
speexrate
    Rate Converter Plugin Using Speex Resampler
jack
    JACK Audio Connection Kit
oss
    Open Sound System
pulse
    PulseAudio Sound Server
upmix
    Plugin for channel upmix (4,6,8)
vdownmix
    Plugin for channel downmix (stereo) with a simple spacialization
hw:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=1
    HDA Intel PCH, ALC1220 Digital
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=3
    HDA Intel PCH, HDMI 0
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=7
    HDA Intel PCH, HDMI 1
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=8
    HDA Intel PCH, HDMI 2
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=9
    HDA Intel PCH, HDMI 3
    Direct hardware device without any conversions
hw:CARD=PCH,DEV=10
    HDA Intel PCH, HDMI 4
    Direct hardware device without any conversions
plughw:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=1
    HDA Intel PCH, ALC1220 Digital
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=3
    HDA Intel PCH, HDMI 0
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=7
    HDA Intel PCH, HDMI 1
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=8
    HDA Intel PCH, HDMI 2
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=9
    HDA Intel PCH, HDMI 3
    Hardware device with all software conversions
plughw:CARD=PCH,DEV=10
    HDA Intel PCH, HDMI 4
    Hardware device with all software conversions
sysdefault:CARD=PCH
    HDA Intel PCH, ALC1220 Analog
    Default Audio Device
front:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    Front output / input
surround21:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    4.0 Surround output to Front and Rear speakers
surround41:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Digital
    IEC958 (S/PDIF) Digital Audio Output
hdmi:CARD=PCH,DEV=0
    HDA Intel PCH, HDMI 0
    HDMI Audio Output
hdmi:CARD=PCH,DEV=1
    HDA Intel PCH, HDMI 1
    HDMI Audio Output
hdmi:CARD=PCH,DEV=2
    HDA Intel PCH, HDMI 2
    HDMI Audio Output
hdmi:CARD=PCH,DEV=3
    HDA Intel PCH, HDMI 3
    HDMI Audio Output
hdmi:CARD=PCH,DEV=4
    HDA Intel PCH, HDMI 4
    HDMI Audio Output
dmix:CARD=PCH,DEV=0
    HDA Intel PCH, ALC1220 Analog
    Direct sample mixing device
dmix:CARD=PCH,DEV=1
    HDA Intel PCH, ALC1220 Digital
    Direct sample mixing device
dmix:CARD=PCH,DEV=3
    HDA Intel PCH, HDMI 0
    Direct sample mixing device
dmix:CARD=PCH,DEV=7
    HDA Intel PCH, HDMI 1
    Direct sample mixing device
dmix:CARD=PCH,DEV=8
    HDA Intel PCH, HDMI 2
    Direct sample mixing device
dmix:CARD=PCH,DEV=9
    HDA Intel PCH, HDMI 3
    Direct sample mixing device
dmix:CARD=PCH,DEV=10
    HDA Intel PCH, HDMI 4
    Direct sample mixing device
usbstream:CARD=PCH
    HDA Intel PCH
    USB Stream Output
$amixer scontrols
Simple mixer control 'Master',0
Simple mixer control 'Headphone',0
Simple mixer control 'PCM',0
Simple mixer control 'Front',0
Simple mixer control 'Front Mic',0
Simple mixer control 'Front Mic Boost',0
Simple mixer control 'Surround',0
Simple mixer control 'Center',0
Simple mixer control 'LFE',0
Simple mixer control 'Line',0
Simple mixer control 'Line Boost',0
Simple mixer control 'IEC958',0
Simple mixer control 'IEC958 Default PCM',0
Simple mixer control 'IEC958',1
Simple mixer control 'IEC958',2