I have Monitor1 on the AVR going to the TV, and Monitor2 going to the capture card.
some receivers ( with me was the same) are only equiped for HDMI main OUT signals on port one, HDMI sub OUT is a kind of dubbed HDMI signal which can be altered into a straight clone/or sub or double sub HDMI out on port 2.
which setting i used, it didn't make any diffrence, spend hours on it.......the ports MAIN and SUB with me are NOT equiped for simultaniously HDMI output when EDID has been asked by the connected device.
it just doesn't work.
what works is a good quality splitter which has no problem with CEC/HDCP and EDID connected to MAIN HDMI out
now no problems anymore, e-ARC i solved in a diffrent matter.