how do you identify blown speakers?

Aftermarket.  When I got the car it was missing the whole center section.  Gone were the center bezel, radio, radio pocket, radio/radio pocket mounting brackets, and all hardware.  The harness/antenna for the radio had been cut.  I asked the previous owner about the missing components (thinking the radio had been stolen).  The radio wasn't functioning properly, so the owner had a neighborhood teen who "knew something about car audio"  take a look at it.  The teen broke the center bezel when trying to remove it (didn't see those screws above the radio) and then cut the harness (guess removing the connectors from the radio was much more difficult).  To make matters worse, the owner threw the radio in the trash (along with the radio pocket and mounting brackets), thinking the radio was faulty.  I got a good chunk taken off the car due to the gaping hole in the center of the dash. 

I called the local Nissan dealer, and all the parts I needed totaled over 350.00, Bose radio not included.  This is pretty steep, considering the cost of the missing items is roughly 1/4-1/5 of the cars value.  I went to a pick-and-pull salvage yard and obtained the center bezel, radio pocket (upgraded cupholder-style pocket...Bonus!!), mounting brackets, all necessary hardware, and a few extra switches (tranny shift mode and hazard) for a cool $20.00.  All the components were in great shape with no UV damage. 

Now that I had the components to fill the void, I had to work on some tunes.  Driving an hour and change each way to work sucks without something to sing along at the top of your lungs to.  I installed an aftermarket Sony deck.  It wasn't bad after I rang out the fourteen severed wires in the dash and bypassed all four amplifiers.