Disconnect the plug at the "subwoofer" under the carpet in passenger footwell - this will disconnect the complete sub & rear speaker & power to the amp. (They're both driven off the same amp, so it's shot anyway)
When you peel the carpet back, you'll see an aluminum plate - once you remove that you'll see the brown sub box - just unplug the connector into it - you can either remove the sub assembly while you're at this stage or just put everything back together the way it was with the connector unplugged. (If you remove teh sub, at least replace the aluminum kick panel to support the carpet & leave the "footrest" intact)
This is much easier than removing all the panels to get to the center speaker.