The wireless variant sounds quite interesting. However, if I read the product description correctly, streaming is only possible from a mobile phone/PC!? Is a direct connection from the receiver (i.e., a kind of wireless speaker) not possible? What initially puts me off is that such a device requires a separate power supply. Then I would have unsightly cables in the dining area again.
You would then also have outlet boxes in the wall with speaker cables.
Can you say more about "making the receiver network-capable"? How do I do that, and what are the advantages? An internet connection for the receiver via LAN/Wi-Fi is at least planned!
Then everything necessary is already taken care of.
Can someone still help with my question no. 3? (Which connectors should I plan (receiver -> wall [connector] -> [speaker cable] -> wall [connector] -> speaker)?) This question is currently very relevant since we are in the middle of the electrical planning. Which connectors do I have to install at the input (wall at the receiver) and at the output (speaker wall)? When I look at 2-zone receivers (for example, Onkyo TX-NR525 or Yamaha RXV577), I sometimes see RCA outputs for Zone 2!? What do I do there?
In the area of receiver/wall or speaker/wall, I would save connectors. Let the necessary speaker cables be pulled in, and install inexpensive outlet boxes. Then the speaker cable comes out of a box in the wall and goes directly to the receiver and to the speaker. In the dining room area, you can choose a variant that accepts bananas (if you only want to have speakers there temporarily; otherwise, like in the living area).
Zone 2 = a second amplifier or power amplifier is necessary (see operating manual TX-NR525)

Alternatively, you can choose an amplifier with more power amplifiers. Then 5.1 in the living room and the last two power amplifiers in the dining room – however, nothing remains for outside. With three zones it becomes even more complex and/or expensive.