Installing 6x9 speakers in 6x8 openings and an amp question...

In my 94 GT I have removed all of the Mach 460 components. I have two Kenwood 6x9s that were from a previous car and I decided to put them in the mustang. I just drilled 4 new screw holes for the new speakers and then put them in. Not much of the speaker is really covered by the metal but I'm wondering if doing this is bad? It sounds great though, much better than the stock speakers.

Also I'm running four speakers off of a 2-channel Alpine amp. The amp doesn't even heat up or anything and there is no distortion even at high volume. I looked at JL Audio's website and one of their system setups is similar to mine. They show 4 speakers: A pair of components up front and a pair of 6.5" speakers in the back. All are connected to a 2-channel amp. Well in their diagram they say that "The rear speakers are passively attentuated using a 25-watt, 8-ohm resister in series" The diagram can be seen here: http://www.jlaudio.com/amps/pdfs/SYS_7.pdf

Where can I buy this resistor (Radioshack sells a 25W, 8-ohm resistor but I have no idea if it's the right one), which side of the wire does it go on? Negative or Positive? The rear speakers are a bit louder than the fronts and I think this is why the resistors need to be installed.

I already figure it out. I installed the resistors and it sounds fine now. I can't just connect one of the front outputs and one of the rears because then the stereo seperation won't be there. I don't give up so easily so I won't "just deal with the rear ones being as loud"