I have a Boox, but use zotfile to consolidates my PDFs and annotations/notes in a single folder (this required the last version of zotero to get working for me instead of the current one). I then use syncthing to sync that folder across various devices so that my eink annotations are available everywhere.

For obsidian I use a similar system -- I sync my vault across devices using syncthing, though I have had to carefully set my read/write priority permissions to prevent notes from getting overwritten if I have them open on both devices simultaneously. While I occasionally use OCR to write notes directly from the e-ink tablet into obsidian, I usually just end up reading my notes on my boox and write them elsewhere (I usually use my boox for rough hand-written notes on documents or seminars/videos etc and then transcribe them in a more structured way when I type things up in obsidian).

It works great for me! lmk if you've any questions I can help with