OK Folks hang on a minute! :-)
The speakers pictured are actually C3 not C5. The difference is the size so if you get a C5 it will be bigger than the other speakers. It will also sound better, but that is a different story!
I would suggest calling FR for a replacement. Try for a warranty as these break very very rarely. But if not, see what they cost then you can evaluate your other options.
And yes, the cover comes off with a small pry tool revealing the mounting screws.
As far as OUTSIDE (or even inside) speaker and amplifier mods, please consider my new company MTX for any needs you may have. We are a 40 year old company that makes auto, home and commercial sound systems.
We have a nice, small foot print, low current draw amp that could be installed easily in a number of applications. If you care about sound quality you will want to upgrade your speakers as well. We have many automotive, home and marine speakers available and if you are into ATV's/UTV's we are OEM suppliers and have aftermarket products for you as well.
Sorry for the commercial interruption, but if we are giving product recommendations, I would love to be in the mix!