it reduces the depth of the speaker by putting the face of the speaker out further from the fender, and with the speaker, the magnet follows.

if you bolt the speaker in as is and the magnet is too big, you will A) Bend the speaker basket... or B) Dent your fender. both very bad.

If you buy your speakers from Crutchfield, the brackets are free.
For your existing head unit that makes 14 watts, you need to go with a smaller magnet... I'd choose these for the front:
http://www.crutchfield.com/p_065SL60/Boston-Acoustics-SL60.html?showAll=N&tp=105

and these for the rear:
http://www.crutchfield.com/p_065S65RC/Boston-Acoustics-S65RC.html?showAll=N&tp=105

They will supply both the front and rear adapter plates and wiring harnesses so they plug in.


The reason I wouldn't recommend the 6x9 for the rear is your power out on the headunit, it won't push the 6x9 effectively...