I purposely shredded my stock 6x9s with my subs. I put the seat up and cranked it up. It ripped the surrounds off the baskets. lol
They werent in the greatest of shape to begin with, but just gives an idea of wut is happening to the rears while u run the sub. The rear channel was completely faded out so there was no actual signal going to the rears when i did this, it was all caused from the pressure of the subs.

 

Older european sedans are bad for this, especially bmw and mercedes, as they usually have a metal reenforcement between the back of the seats and the trunk (i suppose they were trying to cut down on road noise from the trunk entering the cabin) which not only makes it difficult to get bass into the cabin, but also makes your deck-mounted speakers extra suceptible to being blown apart by your subs.

 

will try the sound off, sub on scenario - to see how much they move.

the rest, yeah - would rather do fiberglass than MDF...but yes, lots of work. dammit!

considering i'm just running them off the deck at the moment, think i might hold off for now.