I've tried everything I know how to, including installing/reinstalling the mod. I've tried deleting and reloading the EMC values json file. When I shift-hover over an item, it will state the EMC; but when it's done burning (even diamond) gives me ash.

Check the value of Minium Dust. The calcinator produces minium dust as a percentage chance now (emc of item / emc of minium dust)

Relevant code: https://github.com/pahimar/Equivalent-Exchange-3/blob/master/src/main/java/com/pahimar/ee3/util/CalcinationHelper.java#L14-L33

Thank you so much for your quick reply, and help!

Did it end up working?

Yes it did! My diamonds are now successfully converting to minium dust! Thank you so much!