I've got the db6500's in my car with the stock head unit (for now) they are a big improvement over the stock speakers and a very easy install. (for the tweeters, I took the mounting brackets off the stock ones (pried them off) and used 5 minute epoxy to glue them on the back of the Polk tweeters and they fit right back in the stock holes like they were made for it)

 

Pass seat has 0 room, due to that huge crossbeam. You might be able to get away with it under the driver's seat, but I still wouldnt do it. Throw it in the trunk somewhere.