Your case of repair service is lacking for sure. Have to agree. You’ve already mentioned this, but this is probably due to the lack of parts specific to the AV7706.
No point crying over spilled milk, but if you had asked us for our opinions months ago, we would’ve told you not to buy the AV7706.
We would have told you to get the AV10 or Denon/Marantz AVR that had much better measurements than the old AV7706.
If you wanted something made in Japan, it would be the Denon x4800, x6800 and up and Marantz Cinema 30 and 40.