Avid to compositing package and back

Hi their, I have a couple of projects coming up where I will be exporting sd clips from avid and applying various effects to them using After effects and Nuke.

My planned workflow is to export the offline media as a same as source quicktime, import this into after effects, do my effects and then once I have onlined the footage in symphony, re export the 10 bit digibeta footage and replace inside after effects. Then render the footage from after effects and bring back into avid symphony.

I have been doing a few tests exporting smpte bars from avid and then bringing them to after effects and exporting them back to avid. However I have not been able to do this without degrading the image slightly, I have managed to get the colours 99% accurate but I thought I'd ask if anyone has a problem free workflow, I have not tested this with Nuke yet but am interested if anyone has experience doing this.

Cheers

James