yeah, seems like you would have noticed another component in your check of the wires being grounded.
As for removing the back speakers, on my car it's just four screws that hold the cover on, then 3 or 4 four that hold the actual speakers on so just unscrew those and use a wedge to pull the speaker straight up. Wait,,,,how have you checked the wire connections if you haven't gone through that process allready? maybe this is all useless to you, but hope that helps