OK, everything is going smoothly so far.  Now its time to cut those little spacers.  Because of the way you are mounting the speaker from the back, there is a little space between actually speaker which would make the actual speaker not secured to anything, and it would rattle around and ruin the sound( and I rhymed which is so profound, that tripped on a mound, and hit the ground, which made me come unwound... OK I'm done, sorry. 

)  OK where was I, right, you need to secure the speaker some how, to do this you need to cut the little nylon spacers.  Be careful!! I held the spacers with a pair of pliers and cut them with a utility knife.  These little buggers need to be 1/4 inch.  The length is not the most important thing, but they need to all be the same length for proper mounting.  
you need 4 of these per speaker.  
First picture if showing a cut spacer, and the second is of the spacer on the speaker.