I did a test and installed win10 + kodi 21.1.0 + k-lite codec pack (not sure if that codec pack was needed tho) without changing anything at all with the setup and I was able to get eac3 passthrough to work without a hitch. This means there is nothing wrong with the hardware I guess.
I would very much prefer to use libreelec though since win10 feels so heavy compared to LE and due to some other small annoying things.
I was thinking about trying Kodi forum support but since it actually works with Kodi on another OS I doubt they could help me.
Again, any help or tips would be much appreciated.