Hi
You can try my firmware, 7.1 passthrough is working correctly in Kodi and other apps.
In Kodi - System - Audio, enable all the passthrough codecs your external device supports.
Use the latest Kodi app from here
https://mirrors.xbmc.org/nightlies/android/arm/master/
This is an extract from the Kodi log
2019-12-12 03:53:13.801 T:4353 DEBUG: AESinkAUDIOTrack: Using IEC PT mode: 13
2019-12-12 03:53:13.802 T:4353 DEBUG: AC3 and DTS via IEC61937 is supported
2019-12-12 03:53:13.885 T:4353 DEBUG: E-AC3 and DTSHD-HR via IEC61937 is supported
2019-12-12 03:53:13.972 T:4353 DEBUG: DTSHD-MA and TrueHD via IEC61937 is supported
HD audio passthrough is not currently working on stock Edge-V firmware since the source code hasn’t been updated to include the fixes from Rockchip.