Fantastic! Now, I can export multiplane EXRs.
Now, there's still the problem of how I create and populate those planes. Right now, it's very confusing, to me, when I look at a Merge node, let's say. There's the A layer and B layer and the Output Layer. I've tried all these different combinations and they clearly do something, but I've found no pattern to the behaviour - none which I could really follow. So, maybe some sort of explanation would be great here.
Also, if I simply want to render foreground and background elements to separate planes of an EXR, how do I accomplish that? Right now, I'm finding it very confusing and convoluted. Likely because I don't know the workflow. Coming from Blender, this is very, very different (at least on the interface side). Any help would be appreciated.