Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
Since each plate is done as a layer group (each color has it's adjustments clipped to that layer/color group and no further) to maintain the integrity of each plate/layer group, and not be sent to channels- want to avoid the color shifts... Each layer group will have to me merged down and saved as a tiff. So duplicate a layer group to a new file then merge down, save as tiff.. Rinse and repeat for each plate.
The layers are actually made of adjustment layers and layer blend modes.. It cannot go to channels unless first merging down otherwise you will loose all your adjustments. In the FullSpectrum beer bottle seps you will see that the file was duplicated to a new file for each color in the sep and the layer magic happened from there. So each color was a different file. I agree you can use alpha channels, but for the sake of non destructive practices, duplicate each layer group to the new file, merge down then convert to an alpha channel. So as to keep the original sep intact. So no adjustments in the multi channel file. Just save to dcs and off to rip.