HDMI 0 = 0x05, HDMI 1 = 0x06, HDMI 2 = 0x07. Don't know where HDMI 3 and 4 are coming from. Are you running LibreELEC beta?
At the time of writing I was on a stable 8.2.0 milhouse build. Now I'm back to the latest 8.1.2 version. But no matter which version I install the four HDMI ports have always been there. They have been there since I bought the NUC and installed 8.0.1 on it which was the latest version at that time.
This NUC has one physical HDMI port and one physical Thunderbolt 3 port (supporting USB 3.1 gen 2, Displayport 1.2, 40 GB/s Thunderbolt). Like you I understand that I have "2" HDMI ports, where 3 and 4 came from I don't know. Than again that does not explain why my audio output device says Displayport #0 while the NUC is physically connected with HDMI to my HDMI switch.
Uhm, now that I am talking about this. Couldn't it be that HDMI0/Displayport0 is my physical HDMI port and HDMI1 - HDMI4 are the 4 HDMI ports on my switch? Maybe I'm saying something stupid, but it is just a brainwave :-). By the way CEC is switched off in my BIOS.
Don't forget to create a '/storage/.config/modprobe.d/alsa-base.conf' file and check correct loading in dmesg. Look for the snd_hd_intel 'Applying patch firmware...' line. It will definitely not remove HDMI 3 and 4. I will have to look into that.
Ok. I created the two files and put them into place and rebooted. But HDMI 3 & 4 have disappeared and not 1 & 2. Or in some way 1 & 2 are deleted and the "old" 3 & 4 have shifted to 1 & 2.
mediacenter:~ # aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC283 Analog [ALC283 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
mediacenter:~ #
Display More
One remark though. I did not have the possibility to install the 1.66 HDMI firmware update as stated here. I still have to find a HDMI2.0 capable monitor to do this update.
Erik