Also to answer your first question, the easiest way to tell will be to take the door panel or pillar off and actually look at the woofer. Remember that if you check one and it is not blown this does not mean another on will not be. It is possible that your stock head unit actually blew your speakers due to poor sound quality and you just couldn't tell until you put in the aftermarket HU. Even if none of the speakers are blow, almost any after market speakers will be higher quality and sound better than stock. AND to clarify your speakers are all 6X8s (www.crutchfield.com
) You can also use almost any other size however you will need to use adapters to make them fit correctly, I recommend getting a pair of 6.5s or 6.75s.