OK - here's what I'd try in your Denon. Make sure player is set to bitstream, then -
1. look at your manual, pg. 27. there is a setting, BD Audio Mode. by default it looks like it's set to Mix Audio Output. Mix Audio Output adds secondary audio (commentary, etc) to the audio output and downsamples any DTS-MA that's 192khz to 96khz. the key here is it adding secondary audio...bitstreaming prevents secondary audio tracks from being sent so by enabling this, it may force the player to decode to PCM. try changing this to the other setting - HD Audio Output, which the manual says sends DTS-MA, TrueHD. It also says HD Audio Output disables secondary audio so I think this will allow the player to bitstream.
2. in case that doesn't work, make sure Secondary Audio is also set to Off.
3. if that doesn't work, also try turning HDMI Control off in both the player & receiver. Pioneer uses the HDMI Control feature for its proprietary PQLS jitterfree system in players & receivers, similar to what DenonLink does. while having HDMI Control on shouldn't be an issue since Denon doesn't have the PQLS system, if you get to this point, it's worth a try.
4. finally, if still no bitstream, you might want to experiment with different downsampling rates in the Down Sampling setting, default is 48 khz but you could try either 96 or 192.
I think #1 may likely be your culprit because it strongly implies it's going to add secondary audio and that would force the player to decode as PCM before sending. Why Denon defaults Mix is beyond me...that's counter-intuitive to how most companies implement the output, from my experience. Both Pioneer & Oppo default to bitstream & secondary audio is turned off, the direct opposite. I've also had a 1st gen Panasonic player (the very 1st BD player to hit the marketplace @ $1200!) and it was set the same way...bitstream as default with secondary audio off. Denon may default to Bitstream but then turning on the Mix Audio setting to decode to PCM just may over-ride the other setting...pretty stupid!
if this was your problem, my opinion of Denon just went down several notches for making a dumb decision on an out of the box setup, especially for novices
If nothing works, I'd post in the Blu-ray player forum & ask about your Denon player
Because I can't think of anything else to force your player to bitstream. Or sell the Denon & buy an Oppo player - problem solved
The Pioneer receiver is fine...I'm nearly 100% sure it's your player settings.
HDMI Output - set to bitstream
BD Audio - set to HD Audio
Secondary Audio - set to Off
Down Sampling - try 96 or 192 as last resort
to be perfectly honest, Denon's BD Audio setting seems superfluous because all that's needed is to set the HDMI audio output to bitstream or PCM and the secondary audio to on/off. no other step is needed or used by Pioneer, Oppo, or Panasonic players. Denon made it confusing & unnecessary to do 3 settings to accomplish the work of 2.
Hopefully, this takes care of your problem