Keeping such type of speaker board genuineness is useless for music enthusiast, as one or way the other, you will need to tweak wiring for aftermarket sound system and make small alterations.
Remove original rear board totally and replace it with lasani wood or chipboard speaker board. You don't need to drill holes in body for permanent fix. When genuineness is required, put back original speaker board.
Install Pioneer, Kenwood or some other good quality branded 4 speakers that don't need amplifier, 6x9 or 7*10 size speakers.