After trying for many hours in October, giving up, and trying again today, I was finally able to get root working on v3.5.4!
Many thanks to Renate for their pointers here and in the forums as a whole. I primarily struggled with actually getting the edl utility to work with my device as no matter what I tried (or what version of EDL I used) I couldn't get it to work except at one time.
I eventually stumbled upon a post in the XDA forums from Renate mentioning that some EDL loaders have a timeout that prevents the tool from working in some instances, and sure enough,
as long as I started the EDL commands quickly after putting the tablet in edl mode, it would actually connect to the device. For example,
Code:
adb reboot edl && edl rf flash-backup.img --memory=ufs --loader=q662.elf
is what allowed me to backup all of my system partitions with bkerler's EDL utility on Linux.
Following that, I was able to easily flash my patched boot partition with edl like so:
Code:
edl w boot_a magisk_patched-27000_RNHDQ.img --memory=ufs
After reboot, everything worked as expected! I just had to open the magisk app and let it reboot the system one more time.
The rest of the rooting process is mostly the same as the standard Linux procedure for a Boox device, but if anyone reading this down the line needs extra guidance please let me know.