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I want to export my After Effects render in different layers, some will have alpha values to composite, and stack them in Resolve, keeping the alpha merging as it is in AE.

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Rendering out of After Effects

I've got a background and a glow, which are merged into a composite shot.

Here is the background

Here is the glow (foreground)

And here you can see the composite image, as I want it in After Effects.

I render them in EXR 16bit, rvb+alpha (straight), ACES 2065-1

I have a script that let me set the "straight" option for alpha in OpenEXR for those who are locked with the premultiplied option.

Then I import them back in AE to test them, everything is working fine with the correct alpha interpretation, I got the exact same result as in my composition.

Importing and stack in Resolve

And now, I want to stack them in Resolve so the colorist (who wants the ACES color management for some reasons) can work on each layer. And here comes the problems.

First of all, I set my color management to ACEScc, 2.0 (whatever) ODT in REC709... I disable the tone mapping in Fusion because I saw that it can affect the alpha output. (you'll see why I talk about Fusion later)

I also change the alpha mode for the glow EXR to be "straight" in DVR.

Everything is set, I can now compare my stacking layers to my reference EXR (composited in AE)

This is my composite reference, exactly what I got in AE (except the REC709 general shift between ACES1.2 and ACES2.0 but does not affect the alpha merging)