balbes150, thanks you a lot, especially for your patience that you demonstrate answering user's questions (wich sometimes seems are not adequate)
I want to share my successful experience with my TV Box - Mini M8S II (p212 motherboard and amlogic905X). I turned it into Nextcloud Server/Storage with armbian/ubuntu on internal eMMC.
1. tv box no need dual-booting, it boots automatically in order: USB - SD card - eMMC.
2. i used latest images Armbian_5.88_Aml-s905_Ubuntu_bionic_default_5.1.0_20190607.img
3. i backed up eMMC
4. i flashed eMMC with 'su-' --> './install.sh' painlessly whithout errors. And 1st boot was successful.
5. SSH become lagging. Im using LAN and decide turn off wi-fi totally.
/etc/network/interfaces
uncomment
wireless-mode Managed
wireless-power off
And lags/freezing went away.
The speed and reaction from eMMC is much better than SDcard (even 10 class)!
Spasibo eshe raz, balbes150.