you either have the strength of a 2 year old or you are doing something wrong. the speaker grills just pull up. the gaskets can get "stuck" slightly from the sun, but the covers still pull up relatively easy.
removing the rear shelf will be a waste of time and help you in NO WAY. the screws HAVE to be removed from the top. the only way to do that is to pull up those covers.
those speakers are stock premium sound speakers, they are not aftermarket in any way. don't listen to anyone who tells you to remove the shelf or that they may be aftermarket.