I just found and ran the Entech
Monitor Asset Manager 2.9 utility, and while it must be a little out of date because it didn't report my TV screen resolution capabilities correctly, missing the 4K resolutions, it did report the audio information below.
As you can see, my Sony TV supports 6 channels over HDMI. I have a direct connection to the TV for video display, so it is reading the TV data directly. My audio is sent to a Receiver via a TOSLink connection, encoded as 5.1 DD, but that shouldn't matter in this analysis.
I just set up a MC Zone to play to the TV via HDMI, turned off "Output Format" in DSP settings so it will play PCM, played a 6 channel movie and the MC Audio Path showed 6 channel in, 6 channel out. That was expected because I am using a nVidia 1060 video card, but it shows that the utility reports the TV's capability correctly.
See what the utility, or something similar, reports for your TV. (Assuming you also have a TV connected.) It may also report the Denon x1400 capabilities if you have the HDMI going via the Denon x1400. i.e. PC > Denon x1400 > TV. You had a Blu-ray player, so I assume there is a TV in the mix somewhere. If not, you may be able to find a HDMI analyser somewhere that isn't specific to monitors.
CE audio data (formats supported)
LPCM 6-channel, 16/20/24 bit depths at 32/44/48/88/96/176/192 kHz
AC-3 6-channel, 640k max. bit rate at 32/44/48 kHz
DTS 6-channel, 1504k max. bit rate at 32/44/48 kHz
CE speaker allocation data
Channel configuration.... 5.1
Front left/right......... Yes
Front LFE................ Yes
Front center............. Yes
Rear left/right.......... Yes
Rear center.............. No
Front left/right center.. No
Rear left/right center... No
Rear LFE................. No