How do you get 32-bit float effects to work with an alpha channel?

Question

I make a few bugs and lower thirds, but I'm having a lot of trouble getting 32-bit float effects to correctly export with transparency.
When I make semitransparent animations with bright lighting effects, they look great in AE but I can't seem to find any way to bring them over to Final Cut and get them to look like they should.
I've attached this example of a bug with a screenshot from AE on the left and from FCP on the right. The colors dim and the vibrant blue gradients get flattened into a dull greenish color.
So far as I can tell, all my alpha and color management settings are correct. I've tried endless settings options and codec options to try to fix this, to no avail.
You can create an extreme case as an example by creating a semitransparent shape, cranking the color way up to a saturated superwhite color, and moving it around with motion blur. The render looks pretty much just like a 8/16 bit render, and nothing like it did in your canvas.
I have a feeling the way AE multiplies the superwhite color values with the alpha channel gets "lost in translation" when it is rendered to 4 8-bit channels. Is there any way to get it to look the way it does in the canvas?
Thanks,
Clint

Answer 1

Thanks so much for your ideas. I'd already tried experimenting with a number of color management options, including 'Preserve RGB' and turning off 'Convert to Linear Light' but they didn't fix it. I had also already tried using the "None" option from the codec menu.
I pulled it back into AE, and it looks the same as it did in FCP.
I'm starting to think the issue has something to do with AE rendering to a file differently than the way it renders to the canvas. For example, here's a fast moving 50% opaque superwhite shape in the AE canvas:
I rendered this using Animation + Alpha using Best settings and 32-bit float, and reimported it into AE:
I think the answer may lie in the fact that the first image looks solid white in some places, even though it is 50% transparent. It's almost like the excessive RGB values "bleed" over to the alpha channel. The rendered image (probably correctly) looks grey because it represents white at 50% opacity.
What I want to do though, is find a way to make my render look like my canvas. So it seems I need to do two things to the image:
1. Find a way to increase opacity in areas of excessive white, so that they are not grey in the render.
2. Find a way to "bake" the superwhite colors to a level below 100% white so that they show up in the render.
I tried the "Alpha from Max Color" effect and this seems to get kind of close, but unfortunately it discards other parts of the alpha channel (like drop shadows).
It might also be helpful to know that when I have AE output to an external NTSC monitor (via Intensity card) the monitor shows the exact same artifacts as the render.