Quote from "StudioLive_Series_III_Stagebox_Mode_Addendum_V3_EN_06062018 "

2.1 Routing AVB Inputs

StudioLive Series III mixers route channels in banks of 8. From the AVB Inputs page, you can choose to auto-configure your routing as follows:
StudioLive 32R and 24R:

•• Stage Box Mode. Inputs 1-32 will be routed between the two networked mixers so that they are available on both. The Main Mix and Flex Mixes 1-16 will be routed from the console mixer to the rack mixer.

•• Monitor Mixer Mode. Inputs 1-32 will be routed between the two networked mixers so that they are available on both. The Main Mix and will be routed from the console mixer to the rack mixer but the Flex Mixes will remain local to each mixer.

Note: Once channels have been patched between your StudioLive Series III rackmount mixer to your StudioLive Series III console mixer, they can be accessed by selecting the Network input as the source on either mixer. For example, if you would like Channel 1 on your console mixer to be sourced from Channel 1 on your rack mixer, you must select Network as the input source on your console mixer. In this way, you can access local analog, network, USB, or SD input sources for each channel as needed.

wahlerstudios wroteQuote from "StudioLive_Series_III_Stagebox_Mode_Addendum_V3_EN_06062018 "

2.1 Routing AVB Inputs

StudioLive Series III mixers route channels in banks of 8. From the AVB Inputs page, you can choose to auto-configure your routing as follows:
StudioLive 32R and 24R:

•• Stage Box Mode. Inputs 1-32 will be routed between the two networked mixers so that they are available on both. The Main Mix and Flex Mixes 1-16 will be routed from the console mixer to the rack mixer.

•• Monitor Mixer Mode. Inputs 1-32 will be routed between the two networked mixers so that they are available on both. The Main Mix and will be routed from the console mixer to the rack mixer but the Flex Mixes will remain local to each mixer.




Note: Once channels have been patched between your StudioLive Series III rackmount mixer to your StudioLive Series III console mixer, they can be accessed by selecting the Network input as the source on either mixer. For example, if you would like Channel 1 on your console mixer to be sourced from Channel 1 on your rack mixer, you must select Network as the input source on your console mixer. In this way, you can access local analog, network, USB, or SD input sources for each channel as needed.

Im afraid I need to see some sreen Shot, how to do it, because I have spend many hours to try lot of things And Nothing will work out.

There are some illustrations in the manual, but I also haven't seen any basic description for the procedure. I have seen one video about this theme, but it also leaves questions open. But maybe it can help you:

PreSonus—Digital Patching (Soft Patching) on StudioLive Series III
https://www.presonus.com/videos/player#PreSonusDigital-Patching-Soft-Patching-on-StudioLive-Series-III

As I don't use any Series III equipment my knowledge about the "new" equipment is very limited. Hopefully somebody of the Series III users can give you better answers.