Rear Panels Removed

I did remove the rear panels, in order to see what I would need to do regarding the insulation. There is much hollow space, which will need to be filled. I also removed the speakers and plan to replace them with other 4x6 speakers: On eBay I got Fusion replacement speakers which would fit exactly in the existing 4x6 space of the old panels. But I may actually remove the panels altogether and put my own "furniture" there, so I might have bought other speakers. Never mind, these new ones look like an improvement over the previous built-in ones. I may also replace the front speakers at some point.