Are all speaker relays removable? One receiver with two relays?

Hi there, I mean if all speaker relay COVERS are removable. I have a Yamaha AX-730 and suspect it needs some cleaning. I tried to use two nails as levers to lift the black plastic cover but it seems it can’t be removed. Not sure if I should apply more force, being afraid I may have in fact loosened the solder. Do some speaker relays have fixed covers so they have to be desoldered for cleaning? Or by cutting a hole on the cover for cleaning?

I also find a black box of the same size and shape above the relay (please see the photo) but without any identification on it. What is that?