I recently was asked to quote some headphones for an "Hdmi only" system. I tested the Yamaha avr and Sony 4k TV. I set the AVR to send audio to the TV on the Hdmi monitor out. Then I turned the TV speakers on, and I had sound on every source. So I can just use the headphone output on the TV.

One thing I did not try was a Blu-ray with trueHD or dtshd track and see how it behaved.

Not sure how the denon handles that. I have seen some AVRs that will send audio to the TV, but it disabled audio at the AVR. It was one or the other. The Yamaha I tried it on was an rxv481 I believe. I also tested this with an integra dhc 40.2 and Sony 4k TV.