The polystyrene liner is in three parts in the system 6.
Once you have removed the padding and a few screws the two sides of the polystyrene liner can be removed and there are two cutouts between polytstyrene and outer shell that the battery pack, on one side, and curcuit board on the other.
Also two of the red stud popper fittings is removed and a new ones fitted with the mic mounting in between them.