Hi
I am as many people here will be, all too familiar with this problem.
As you may know straight alphas are nasty and do not provide a “clean” key, however at the same time the AVID really doesn’t know how to deal with a premultiplied alpha.
By what you’ve said you know this already, and sadly until AVID get their act together on this, you will have to (at least to my knowledge) resort to things like swapping fills or take footage into AFX.
If you do go with the later at least (file size permitting) you can export 1:1 from adrenaline and render back as an uncompressed meridien quicktime, and wont loose too much.
Lets all hope AVID make some changes regarding alphas soon.