What I'm saying that the JBL 2426 response curve looks like this:That's what it will look like with a first-order crossover too. It's difficult to add compensation to a first-order network because filter peaking isn't cooperative for what you're trying to do. And you have to watch the power.
Use a π crossover, and this is the response you can expect:
Response above 4kHz is still reduced, but it forms a shelf that remains pretty flat from there on out.