Boy you really dove in head first! I don't have tidal, but I bet you can load a tidal app on your apple TV. If not, you could send it from an iPhone to the apple TV via Airplay. You could also get a lightning-camera adapter and USB cable and plug into your receiver assuming it has a USB Input.

1. You cannot upgrade the DAC chip in any consumer prepro or AVR as far as I know.
2. Are all your side/surround speakers in the ceiling? Not ideal for video and worse for music, imho.
3. I prefer QOBUZ to Tidal but don't take my opinion or that of any other about this. All the audio streaming sources have free trial periods and you should try the obvious candidates and decide for yourself.