The way I explain the two options to people is this: Creative Cloud Files is for saving entire documents to a folder that can be viewed in a web browser and shared with virtually anyone. This can be helpful to get approval from a client, or to allow anyone who has access to download then file in a variety of different formats. You also have the ability to allow users to comment on the files. Creative Cloud Libraries is for sharing "assets" with other users within the Adobe applications. Yes, these can also be viewed via a web browser but these assets are most useful for making text styles, colors, and objects available to users within the Adobe applications. Getting back to your original question… To achieve what you describe in your original post, you would want to export your Illustrator artwork as .png files, then open them in Photoshop and using the Move tool, click on the canvas and drag the image to your CC Library. This will add that .png file as an asset to the library. From there, you can share this library with other users by clicking on the panel menu and choosing Collaborate. As long as they are Creative Cloud subscribers, they'll get an invite and once they accept the invite, they'll have access to the library.
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