found these, didn’t read them, hope it helps.
https://carvinaudio.com/blogs/audio-education/proper-power-up-sequence-explained#:~:text=So%2C%20proper%20power%20up%20sequence,power%20amps%20to%20the%20speakers.
https://www.sweetwater.com/insync/power-power-off-sequence/
In a long ago setup I had the same issue. Some equipment can and other equipment does not send a signal to the speakers. Went on for years, didn’t damage anything (luckily?)
Some power protection devices have timed delays for activation of individual outlets dedicated for specific equipment to eliminate that problem. Also, timed sequential turn off.
Amazon Power Sequencer