Take your time. I look forward for your mod and see what kinds of sound improvement. I'm hoping your mod add more body or overtones for timbre, specially in midrange. From what I read so far, the brightness is a much easier fix with a resistor to crossover.
Are you also moving the crossover point higher like how Cauldron point out in his research to bring the midrange's presence forward?
Here is the comparison between JBL 590 and RP-8000F. I love the smoothness and dynamic of the JBL but not as alive as Klipsch. JBL's midrange is more nature with the right amount of body or overtones to the tone.