I am getting the exact same problem, I also have the TX-NR636. When I tried using the onkyo command, I can discover it, the onkyo-eiscp script breaks and gives this error:
/config # onkyo --discover
TX-NR636 192.168.0.10:60128 0009B0D8562B
/config # onkyo -n 636 system-power=off
Traceback (most recent call last):
File "/usr/local/bin/onkyo", line 8, in <module>
sys.exit(run())
File "/usr/local/lib/python3.8/site-packages/eiscp/script.py", line 179, in run
sys.exit(main() or 0)
File "/usr/local/lib/python3.8/site-packages/eiscp/script.py", line 136, in main
response = receiver.raw(iscp_message)
File "/usr/local/lib/python3.8/site-packages/eiscp/core.py", line 470, in raw
return filter_for_message(self.get, iscp_message)
File "/usr/local/lib/python3.8/site-packages/eiscp/core.py", line 270, in filter_for_message
raise ValueError('Timeout waiting for response.')
ValueError: Timeout waiting for response.