Sorry, I don't have a guide as such, I just played about with my mxq pro v2 with a few twrp's I had lying on hard disk and one of them booted up the box and let me make a backup. Easy enough, run twrp from toothpic then when it boots, select backup (by default it selects boot data syatem partitons) and choose usb otg or sd or internal to backup.
unsure of the T2 model as it was bought 2nd hand and was really laggy, may have been a clone??? who knows. Can't find it in droidbox shop, sold it on now (
The M8S is a generic chinese box with the s812 soc but, as you've sussed, AlexELEC will run on any armlogic chips.
Outside of Kodi you can reboot to IPTV app, Nintendo games emulator or reboot to droid.
I'm not a programmer but I got fed up waiting for Droidbox updates as the imxq pro v2 has dual boot with LibreElec and it looks like some of the LibreELEC update functions have been coded out of the installation so you can't update via system settings / updates. have worked out that I can download the tar files for the current build then connect to LibreElec via Samba to drop the tar file in the updates folder. Again, work in progress and don't really care if I break the box as I have original ROM backup.