Question about Panasonic DP-UB9004

Yes, if you connect the player directly to the AV via HDMI (min. 1.3), its audio signal is also transmitted loss-free via HDMI and the AVR does the rest 👍 The AV will then output audio correctly depending on your setup.

The audio output is not unimportant, with the advantage that the Blu-Ray player can of course play all Lossless sound formats, but yes the AV receiver only has to accept the information and play it back accordingly.

According to Panasonic, it is the best of all time, but I think it doesn't matter about the sound, as long as the digital is output by the player, even the best Blu-ray player can't make the sound any better. With the picture, maybe, but then you also need a TV that can do that. Of course, it's the Blu-ray player that determines what comes out, together with the sound formats that the streaming portal or the Blu-ray provides.

AV receivers can sometimes also process sound formats with cross upmixing, i.e. you can receive something sound-wise from the player and the AV receiver then converts the signals into an object-oriented sound format. It depends on the AV receiver.