Blackie

I find your research interesting.  I don't have this particular box (I have a TX3 based on the s905x3 cpu).  If you provided links to the source code for the dtbs (i.e. the .dts files) I'd be willing to at least look at the source code to see if anything jumps out.  Also since you want the gigabit ethernet working, do you know what ethernet chip your box has installed (i.e. could you open the box and take a picture of the board and especially the ethernet chip)?

Anyone tested "SCISHION V88 Piano" box? https://www.gearbest.com/tv-box/pp_1064854.html
Gigabit ethernet, 4GB ram, nice thermal case design, DRM widevine level 1, ... seems to me like a nice RK3328 box.
The smaller SCISHION box is booting from the card, not sure about this one.