Those pics don’t look right. Pic #1 shows Zone 2 as Select Automatically, not Surround Back. Pic #2 shows Large Surround speakers up front. Check the Surround Layout setting. It should be set to Rear, not Front. If set to Front, Surround speakers are supposed to be placed up front and Surround Back will not be selectable at all. You want a configuration pic that looks like the one below, sans Sub and Presence speakers.
View attachment 63338
Remember, you are not concerned with the configuration matching your current setup. You just want to see if a signal is output from the Surround Back terminals when connected to your front speakers and configured to 7.1 since you claim no sound was output when configured to 5.1 bi-amp. Make sure Zone 2 is OFF. If it is ON, you will not get sound from the Surround Back terminals. Once configured correctly, play something using 7ch Stereo and see if the Front speakers produce any sound.