To make my CMY negatives for Gum printing, I go to Mode-Mulitichannel-Split Channels (I use the “C” negative to print with black pigment and a short exposure at the end rather than making a separate “K” negative).
The image in the multichannel mode (left) is an approximate preview of what the final gum print (right) will look like.
I adjust the image before the Multichannel step by increasing the Cyan (30-45) and Saturation (around 30). The increased Cyan and Saturation image (left) will look strange compared to the original image (right).
Without altering the image before the Multichannel mode produces a muddy red/brown multichannel image (left) as compared to the multichannel image with the increased Cyan and Saturation (right).
I find that altering the Cyan and Saturation (top left) renders a color balance in the Multichannel image (top right) that produces a gum print (bottom left) that matches more closely to the original image (bottom right).