I have just been testing with excel 2016, and it looks like it really REALLY doesn’t work.
This happened when Microsoft went from 2010 to 2013: the underlying programming model changed the way Excel can be embedded in other applications. In the case of 2013, it just means that the Excel window floats away, and can’t be docked inside eaDocX. But it still works.

Well now it looks like this problem has gone away with 2016, but lots of other new issues have appeared. I can get the basics to work, with some fiddling, but the Excel UI remains un-responsive: I can’t edit anything!
I tried to use Excel 2016 with the Sparx equivalent, and their excel exporter freezes-over as well.
Looks like we have LOTS more work to do to make this work!

In the meantime, I will update the system requirements to sat that eaDocX, as of version 3.7, DOES NOT SUPPORT EXCEL 2016.
Sorry about this, but we are stuck in the middle of two very large organisations – Sparx and Microsoft – who constantly change how they do things, and we have no control over either of them.
Sorry 🙁