Hi, I am new here, so bear with me. I am having trouble understanding why it seems every speaker I look up on Crutchfield (either the 6 3/4 or the 6x9), does not seem to be compatible. These are the right sizes for a 2002 Xterra, right? Any ideas?

the standard size that fits in the doors are 6 1/2" and thats a standard size speaker throughout the speaker industry,I put 6 1/2" in my doors ,and the rear are a standard 6x9 " fit.
I have an 02 also.

Regarding the 6x9 speakers for the rear cargo area, I believe mounting depth is the main reason they don't list anything. While I'm pretty sure many people have worked around the problem by putting in some sort of spacer, the need to do so most likely would preclude them as being considered "easy fits" by Crutchfield.

I remember some guy mounting 6x9s and since they wouldn't quite go flush he pounded 'em in place until they were. Then he discovered the nice semi-circle in the quarter panel from the magnet pressing from the inside...

my kenwood 3-way 6x9's fit just fine.