Mecool m8s plus (s905x2) box with wifi RTL8188F.

&ethmac {
    status = "okay";
    phy-handle = <&internal_ephy>;
    phy-mode = "rmii";
};

SEI510 uses the internal Ethernet PHY embedded in the SoC itself so as long as that's present in device-tree Ethernet works. The X96-Max dtb uses external PHY which requires different content and the correct compatibles to work. The SEI510 has special audio config though, which will not align to the config used with most TV boxes.

For WiFi, the SDIO bus supports discovery and probing by the kernel so as long as the bus is enabled (and is most device-tree files it is) the chip can be seen and matched to a kernel driver and used. I've added the RTL8189ES/FS drivers into my private LE sources for a while so the needed driver is present in the image. Those vendor drivers are deliberately not present in the main LE releases, and that's not going to change. You can find the packages here: https://github.com/chewitt/LibreELEC.tv/commits/amlogic

It should be fairly simple to create a device-tree for the box. Start with the X96-Max and just change the Ethernet config.

Have a read of this: https://wiki.libreelec.tv/development/git-tutorial

In short, you need to create a diff patch that patches the kernel sources either modifies the x96-max dts file or (better) adds a new dts file for your box. Clone Linux kernel sources from https://github.com/chewitt/linux/commits/amlogic-6.1.y then create a new branch and make and then commit changes. You can then generate the diff patches from the commits (git format-patch ..) and copy them into the LE buildsystem at projects/Amlogic/devices/AMLGX/patches/linux/ then rebuild the image so the patches are applied to kernel sources and included in the built kernel. If you modify the kernel build folder direct; a) respinning the image will not pickup the changes, b) if you force the kernel package to be rebuilt this will remove the build folder and unpack it again from sources overwriting your changes.