Audio Systems: maxima speaker change, speaker change, bose system

Question
I have a '92 maxima with original clarion speakers that are blown. I am trying to replace the rear deck pair. I purchased a pair of 6x9's that said they fit that year. But when pulling off the cover I noticed that the speakers are not 6x9, they are smaller. Do I need to cut a larger hole to fit the 6x9s? Will the original wiring even work? The connections are different.
I thought of mounting them from underneath but the area is not flat. Any advise?

Answer
You probably will either have to cut the holes larger with a power nibbler (Makita makes a good one) or just take the speakers back and exchange for the right size. Most japanese cars use 6.5 inch rear, not 6X9.
http://www.installdr.com/InstallDocs/Nissan/PDF/647037.pdf

And if you are unlucky enough to have a BOSE system, they are different again.

The wiring will always work, no worries there.