Air space for 6x9

From what I understood, 7x10 was just slightly oversized 6x9's, and a 6x9 would fit fine an any hole made for a 7x10...   Like a JL 6 being a 6.5 .......Either way, I strongly vote against this idea as well. Why are you putting 4 6x9's in the back of a vehicle?? Your soundstage will be terrible, not to mention, 6x9's??  The only reason I could see you doing that would be if you were going for an SPL set up.... because your quality will be crap.... but then... why would you use 6x9's for SPL?? The only logical thing that I can come up with, is to do this as a joke, throw a whole crap load of 6x9's in a car with a LPF on, and show up at a dB drag.... even that would only be funny for the first 4 minutes.so..... yeah... why are you doing this?

when you got a whole lot of bass coming from the trunk you need alot of highs to even it out. So what would you use other than 6x9s, I hope no 6 1/2s cause they suck compared to 6x9s come on!!!!!