I have the bose 6x9 inch speakers in the back. I want to put a pair of infinity 6.5 inch speakers in there. Is there a place where I can buy the cutout sheet that I can use self threading screws and mount hte six and halfs in the middle?
Make them yourself. I did this about 5 years ago, takes about 20-30 minutes. Just use a thin sheet of mascinite(not sure if the spelling is right) and use your 6x9 as the outline. Once you cut it out and drill out the screw holes then mount the MID on the side close to the seat belt and mount the TWEET closes to the middle of the car. 6.5 mid and 1 inch tweet will be somwhat "snug" but take your time and you should be fine.
I thought I could get the template printed sheets somewhere for about 10 dollar a pair. I heard that in the past.. Anyway, your idea of making it out of masonite is not bad either. I will try that. The tweeters are mounted in the middle of my 6.5 speakers, so no problem there.