For the stock ir remote you need to copy the remote.conf file for your box into the .config folder and reboot.
The External USB receiver should work when plugged into a working USB port of your box.
I have 2 that always worked on OpenElec and LibreElec (generic Linux)
This one is from Microsoft (Driver: mceusb, table: rc-rc6-mce)
I also tried my original HP receiver. Same result, plug and no play
Plan B would be to open the H96 pro plus and find the IR receiver
Then extend it with an IR eye I have spare here
So far I didn’t open it but I have the 3GB version with just 2 USB ports
Starting top left I see reset, usb, usb, power, AV, HDMI, Spdif, LAN
And below the SD card
Top left are 2 LED’s. And blue power LED or maybe 2…
If it’s 1 then the other one might be the receiver ?