I did find out how to do everything. I posted a write up of my complete process. Search for posts by me to find them.

To answer this question specifically you do need to remove the rear seats to get the speaker grills off. They slide towards the front of the car. On the outside of the grill there is a tab, be careful to keep the grill low until that tab clears the hole it is in.

If you have other questions feel free to PM me.

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86 300 SDL - Vesuvius

96 SL 500

Assumption is the mother of all screw ups.

Do not go gentle into that good night. Rage, rage against the dying of the light. - Dylan Thomas

All that is necessary for the triumph of evil is that good men do nothing - Edmund Burke