Going through serious gum withdrawals so I spent a couple of days reliving the agony. I’ve been going round and round with the separation technique, but finally proved to myself the multichannel and RGB give identical results (at least on CS4), while the CMYk ( K layer as needed) method tends to give more saturated isolated colors. This duck image illustrates that pretty well in the yellows, oranges and reds- note the duck body and bill. The channels are in order left to right- C, M, Y. I do print the K channel with ivory black, to build the shadows back up.