There are no plans to remove the current limited number of realtek modules (or to add more). If we do remove a module it will be because we can switch to an in-kernel module. Some of the older Realtek cards are supported in-kenrel now, but the drivers still aren't great and Pi Foundation feels there are too many older Pi users with the official adapter for us to switch. Realtek are more actively engaged in upstreaming support for latest/next chips now so in the future the situation will improve for new devices, but I suspect there will always be a gap for recent-past and older cards.
LE does not support pre-boot configuration of wireless details, it's not a requirement for our userbase (the other 99.999999% of it) so your options are to connect via Ethernet (direct cable between two devices with 169.x.x.x addresses is fine, it doesn't need to be a proper network) or use Raspberry Pi OS via NOOBS which can support pre-boot WiFI configuration.
LE uses 5.10+ kernel and Allwinner will be using a BSP kernel (usually 4.9, 4.19 or at best 5.4) so any modules you compile will not be compatible.
documentation/cm-emmc-flashing.md at master · raspberrypi/documentation · GitHub
^ this is the procedure for mounting the emmc storage. In my experience the Slice box is a bit tempremental about connecting to the host so don't be too surprised if it doesn't work first time. Once the emmc is mounted as a local disk you can flash the LE image using any USB/SD image writing tool (ours, Etcher, Win32DiskImager, etc.).
I thought wireguard: Regular reresolve endpoint address · igaw/connman@90592f7 · GitHub should have solved this issue? If not I might need you to explain the problem properly so I can replicate it and nag the ConnMan devs.
marantz using the settings add-on to set the regdom?
Montellesse's repo is forked from the upstream Kodi repo so it shouldn't be much harder than a one-line change to package.mk to build with a different PKG_VERSION using the githash of the last/latest commit in his repo. Also set PKG_SHA256="" .. and build. It's simple enough (and our build-system is simple enough) that the community can step up to do the building insteaf of increasing the output burden on a small number of developers. Hopefully the code for this goes upstream at some point..
Each time I see people building servers and NAS and wading into lots of complexity I am reminded that I too used to do that, and then eventually I ran short of time in life and bought a Synology box. I have since forgotten a vast amount of trivia about running a NAS, because I no longer have any need know NAS trivia. It runs itself without any involvement from me beyond sanctioning the occasional update and I appreciate the value in someone else spending their day-job on fixing functional and security bugs and providing a simple-enough GUI on it all.
Anyway.. it sounds like you need a NAS, so think about getting one instead of frankensteining Windows with awkward share arrangements.
In limited testing the revised alsa conf appears to prevent machine gun noise on GX boards. It's a workaround not a fix, but until somene figures out where the buffer underrun is occurring it will save some speakers (MGN is nasty). I'm currently hoping that LibreComputer will fund further work on multi-channel audio in the coming months, but this is still to be confirmed. Martin B is also poking around in the AIU driver to add support to Meson8 hardware, which may also help.
Stop Kodi, remove /storage/.cache/connman and reboot.
I never really used the NOOBS based recovery stuff so I can't really guide you on how to work it, but the best option for LE use is to connect the box to a PC and (as per the comment you've quoted) write the image directly to emmc overwriting NOOBS.
giancai best to ask for help in a forum like freaktab that specialises in Android devices and ROMs .. we're not one.
Images we (almost) support use the mainline kernel: linux/arch/arm64/boot/dts/amlogic at master · torvalds/linux · GitHub
Images with 3.14 or 4.9 kernels are no longer supported.
mglae .. read post #1 the user has Intel/nVidia cards and the nVidia drivers definitely aren't built-in 
Images from ~ 5 mins ago have much improved audio on G12A, G12B and SM1 devices. You should be able to play all media without encountering static (all the multi-channel audio files I have work) and multi-channel audio channel mappings are fixed. I have disabled IEC958 devices in the alsa conf as I get static pops that don't sound tweeter friendly when trying to use the "HDMI" device or pass-through; the drivers are not ready for this yet. Select the "Analogue" card listed immediately above pulseaudio.
The same changes are in the GX device images, but I haven't done any testing to see if the revised alsa conf has a positive effect on the "machine gun noise" (buffer underrun) problem in the AIU driver.
tavoc The "box" image is for booting devices with vendor u-boot, the "khadas-vim" image has mainlne u-boot and is for writing LE to internal emmc (overwriting the vendor u-boot).
echo "sleep 30s" >> /storage/.config/autostart.sh^ this is wrong, it should be "30" not "30s"
No plan to switch to pulse. It doesn't support HD audio formats properly (despite release notes that hint it does).