Concerning removal of the insulation:
The batt insulation, that fluffy pink or white stuff, loses effectiveness when squished down. It should remain as fluffy as possible to create the little trapped air chambers that makes it work. Cut out just enough to make the speaker fit, but no more. If possible, scoop it out, leaving it intact behind the speaker. If not possible, then 1 piece of the rigid board insulation that is the proper thickness and affix that behind the speaker. Don't leave any air gaps, but fill everything in.
