Hmm sorry this is getting offtopic but you seem to be able to help me
I can follow your instructions but what I end up with is only RGB channels with the transparent areas 'deleted' from the channels. Most artists require the alpha channel to be seperate from the RGB so it can be painted onto.
If I attempt to save as PNG while I have my ARGB channels intact, photoshop cleverly unchecks & greys out the 'Alpha Channels' checkbox. It also annoys me with this message: "Some of the document's data will not be saved using the chosen format and options." Argh! I tried the SuperPNG plugin and that doesn't seem to help.
Do you know of a plugin that lets you save and load the PNG with the alpha channel intact? The nvidia DDS plugin does this perfectly.