Path prefixes will probably work, but I encourage you to consider restructuring the application. It is becoming more and more common to merge the admin controllers with the public controllers, and this is one concept that is at the heart of REST. Instead of splitting up controllers based on how they are accessed, split up controllers based on their funcitonality.
If you read the first article you linked to again, they are now making every controller handle both the admin and public side of the site. This works very well if both the admin and public sides of your site have similar functionality and views. If you want the two sides of your site to be completely different, than this may not work well for you - and that's okay too.
In your case though, it looks like you have an admin controller managing three models: tags, users, and news (might want to rename this to something which can be pluralized). Chances are, if you are following a RESTful design, you have publlic controllers which manage those same models. Try removing the admin controllers completely and moving that functionality into the public controllers. Of course make sure the admin functionality (such as deleting models) has authentication so it can only be accessed by the admin.
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