The report tells us your ASUTek VC66 has only the analog device recognized as sound card-0 (an ALC255) also with an HDMI (Codec: Intel Kabylake HDMI).
I do noted an error in the dmesg whic may (?) be relevant ?
5.066308] snd_hda_intel 0000:00:1f.3: failed to add i915 component master (-19)
and a series of other HDMI messages:
5.085228] <ffffffffa045b469>] snd_hdac_i915_register_notifier 0x29/0x30 [snd_hda_core]
5.085238] <ffffffffa089ccb4>] patch_generic_hdmi 0x2b4/0x6b0 [snd_hda_codec_hdmi]
5.085246] <ffffffffa0542435>] hda_codec_driver_probe 0x65/0xf0 [snd_hda_codec]
5.085250] <ffffffff8146cca7>] driver_probe_device 0x1f7/0x420
--
5.086206] --- end trace 42025597258258d2 ]---
5.089339] input: HDA Intel PCH Mic as /devices/pci0000:00/0000:00:1f.3/sound/card0/input11
5.089379] input: HDA Intel PCH Headphone as /devices/pci0000:00/0000:00:1f.3/sound/card0/input12
5.089412] input: HDA Intel PCH HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:1f.3/sound/card0/input13
5.089445] input: HDA Intel PCH HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:1f.3/sound/card0/input14
5.089478] input: HDA Intel PCH HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:1f.3/sound/card0/input15
also in aplay I note the HDMI detected:
!!Aplay/Arecord output
!!--------------------
APLAY
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC255 Analog [ALC255 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
**card 0**: PCH [HDA Intel PCH], **device 3**: HDMI 0 [HDMI 0]
Subdevices: 0/1
Subdevice #0: subdevice #0
**card 0**: PCH [HDA Intel PCH], **device 7**: HDMI 1 [HDMI 1]
Subdevices: 1/1
Subdevice #0: subdevice #0
**card 0**: PCH [HDA Intel PCH], **device 8**: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
So it reads your HDMI could be hw:0,3 or hw:0,7 or hw:0,8 .
The HDMI does not show up in the mixer thou - and that is unexpected. Am I correct that this HDMI is on the motherboard ? I’m wondering if maybe you have an inappropriate setting in your BIOS ? Are there any relevant BIOS settings for HDMI ?
Out of curiousity, do any of these commands (copied into an xterm or konsole as a regular user) give sound via your HDMI ?
aplay -D plughw:0,3 /usr/share/sounds/alsa/test.wav
or
aplay -D plughw:0,7 /usr/share/sounds/alsa/test.wav
or
aplay -D plughw:0,8 /usr/share/sounds/alsa/test.wav
Searching the Internet on “Intel Kabylake HDMI alsa” and I see a lot of people having problems with GNU/Linux and this hardware. One bug report, for example, noted until after the power management puts the display to sleep at least once there is no sound. Upon waking the monitor sound is restored. That is VERY speculative …
I have read of users with this hardware clearing pulse audio settings which helped. ie emptied the directory under /home/username/.pulse and also emptying the directory under /home/username/.config/pulse (if there is such a directory - there may not be such) and then rebooting and testing. Again that is VERY speculative.
This does not read to be an easy nut to crack.
Let us know if any of the above aplay commands work.
.