Okay, this can get a little frustrating at certain parts BUT, it's not too difficult to do. The worst part is putting it back together:
First pull down the seat obviously and remove the 5 pegs that are holding this lip down. Once the pegs are out you just pull the lip down and it slides off easily
Here is a pic with the lip removed:
Once you get the lip off you need to take the side pillars off, to do this get a fine screwdriver and pop these little airbag emblems off
Under these covers is a bolt that you need a #10 socket wrench for if I remember correctly. Just take them out and then pop the pillar out. They come off with little resistance.
Next thing you can do is detach the rear deck and then peel the seat a little bit and you can lift the whole rear deck over the seat.
I don't have pics of my removing it but you get the idea and should be able to see what I'm talking about once you get there. Like I said it's not too difficult to do.
If you have problems getting the rear deck up you can go into the trunk and pinch the pegs and push them up so you can get the deck up.
(The white thing is the peg obviously)
Then once you get the deck up disconnect the brake light (you should be able to reach your arm under and unclip it, it's really easy to disconnect) and pull the deck down into your back seat.
From there you can do whatever to your speakers.
By the way, be careful when putting the deck back because the clips are delicate. I broke one on accident but it still fastens just fine.