[riccardo]

Hi guys, I´m dealing with similar Dolby+ EAC3 problem as the guy above. Files with Dolby+ EAC3 play fine only if no file with HD audio format (DTS-HD|XLL|X|Dolby TrueHD|Atmos) was played before in the current boot session... 

Hello, looks I'm not the only one having this problem. So far I also narrowed all the other problems with audio passthrough to this single one (no EAC3 after HD audio). All the other audio issues I mentioned before were caused by currupted or somewhat wrong files.
My AVR is ONKYO TX-SR608 and I think it is probably the same age as your DENON. A friend of mine, who works for a local electronics repair shop, told me that there is quite a possibility that such AVRs have the same or very similar HDMI input processor chips therefore they might behave the similar way in this case.
When EAC3 stops working I sometimes try not to reboot NUC but to turn the AVR off and on again but it never helps. If only there was a function to quickly reset the HDMI status to the same it was in after fresh boot (without rebooting the NUC of course). From my experience there is no better version od LE9 than current as for the audio passthrough compatibility. I remember that some testbuilds from July/August were not able to passthrough DTS HD correctly - I used to see "Multichannel" instead of "DTS HD MA" on my AVR's display, DTS MAtrix caused the video being jerky, but it's all now fixed. Well maybe some of those older builds could process EAC3 better though. I'll try to find it too.