Minix U9-H would be better for 4K, but using LibreELEC instead (vs. its stock Android OS). Thanks to @wrxtasy's work on LE. Not plug-and-play, but the LibreELEC "thingy" isn't hard to do...
1. Get a good quality mSD card (
like this one)
2. Download
this LE image, then extract it to get
LibreELEC-S912.arm-8.2.4.1.force.444.10bit.img
3. Insert your mSD card into your computer's SD/mSD slot and
use this app to burn the image to the mSD card
4. Find the correct .dtb file for your U9-H (or whatever AMLogic S912 box)
here, download it & rename it to dtb.img. Copy this over the the mSD card, replacing the default dtb.img there
5. With U9-H unplugged, insert the mSD card into box, connect ethernet & HDMI cables, and turn your TV on to the right input
6. With a pin in the U9-H reset hole (hold it in), plug in power. Let go of pin once you see LibreELEC logo on the TV
7. Follow in-screen guide to finish setting up LE, then go into Kodi settings and find your box's IP address
8. Go back to your computer and download the
LibreELEC-S912.arm-8.2.5.1-444-1000nits.tar update
9. In Windows/File Explorer's address bar, type in
//your.box.IP.address (actual IP address from step 7) and press enter. Find the Update folder, and copy over the .tar you downloaded here
10. Go back to your U9-H and reboot
11. Go to Kodi settings > AMLogic, and enable these top two options... done!
You need not use a U9-H... a cheaper S912 box from Mecool, Tanix (I have a TX92), etc. should work as well (or almost as well). Ask which box
in this thread here or
this one at LE forum.