A few years ago, we had 6 homes where the contractor used that kind insulation. Was a surprised when it came time to come in and install the speakers. Though it generally kept it's shape when drywall and then needed insulation was removed for the speaker, sometimes the stuff just kept falling out.
What we ended up doing was pulling out what was needed, along with enough to create about a 6" cavity above and below the speaker. We then stuffed in a bit of standard "Pink" batting insulation to still allow for the needed cavity, keeping any additional blow in insulation from falling down on the speakers.
"if you can't find the answer to life, change your questions"