@Bones
Try this:
Harmony 600/650/700
Press and keep help on Harmony remote for get advanced delay fixing mode
https://support.myharmony.com/en-us/adjusting-a-devices-power-on-delay
Harmony Ultimate, Home advanced delay fixing can get direct from menu
https://support.myharmony.com/en-us/adjusting-a-devices-input-delay
Select JVC 790r device, Change Delay, Power On Delay and set 10 sec delay or more if need.
On Activity set power on order
JVC DLA-X790R
Yamaha
HiMedia
Possible Yamaha need also adjusted power on delay.