[p750mmx]

The Intel spec's page says which max resolution is supported when using a specific output. This is not CPU/iGP related, it is output port related. You can see those specifications with a lot of other Intel CPU's. My Shuttle Kaby Lake barebone (with i3-7100) has 3 HDMI outputs, 1x 2.0a, 2x 1.4.. The 2.0a port uses the LSPCON solution.

The Intel ARK pages discusses output ports only for the CPU like your i3-7100 (or my 7260U),  but not for the chipset like your H270. This made me believe that the output port features are actually a feature provided by the CPU chip and not the chipset - except for the external LSPCON. This is also what the Intel HDR whitepaper seems to suggest:

https://www.intel.com/content/dam/suppor...ePaper.pdf

Alas, i do not understand further details. From the fact that your motherboard has 3 * HDMI, it seems to me as if the Intel CPU/GPU chip could have 3 equal ports that could be configured for HDMI up to 1.4b or DP up 1.2 or eDP. And when HDMI > 1.4b was needed, then the motherboard would need an LSPCON.

Its also unclear to me if the DP port on my PC is actually ++DP, aka: would support a passive DP->HDMI adapter/level-shifter. I guess this would have to be something to be supported by the Intel GPU/CPU chip output port too.

HDR = HDCP2.2 = HDMI 2.0a as a minimum, the Windows version of Kodi (18) doesn't output HDR as is. 

Right.

The Kaby Lake Intel NUC seem to have MCDP2800 LSPCON which claims support for HDCP2.2 HDMI.
Do you know which LSPCON chip he DH270 has ? 

A quick reply to the last question. I couldn't find the answer at this moment.
It's a http://www.megachips.com/products/displayport/MCDP28x0 or a https://www.paradetech.com/parade-techno...onverters/ (PS175).

I could not get HDR working with a DP1.2 > HDMI2.0 active adapter on an previous Kaby Lake system that did not have a HDMI 2.0a port. It works with the system in my signature (not in Kodi though).

Of-course an internal iGP has it limitations, I would only wanted to point out the limitations of a graphical interface. As an example;
- HDMI 1.4 doesn't go any higher then 2160p@30Hz and never supports HDR
- DP 1.2 goes up to 2160p@60Hz (or HDMI 2.0a with converter)
- minimum CPU for HDR is 7th generation Core CPU (Aka Kaby Lake) and HD 630 graphics (as I recall).