'07 CR-V EX-L AWD
Welcome to the forum! You are correct. Different trim levels come with different radios, and the lower level models do not have the necessary wiring harnesses for the upper level head units. Undertaking this would be a bottomless money pit and headache. You'd be far better off to go aftermarket. There are tons of far better than OEM quality audio upgrades in many price ranges. Moving this to Mobile Electronics. Take a look through there, and visit crutchfield.com. Byt the time you finish with all that you will be much better informed on what is possible. Let us know how you go.