The PR6510CS are 2.7Ω and 88dB sensitivity, the PR6502IS is 3Ω and 93dB, and the Kicker KSC3504 is 4Ω and 88dB. For comparison our speakers are the older [PR6500CS] (3Ω and 93dB), the PR6502IS (3Ω and 93dB), and the JBL GTO329 (3Ω and 91dB). The slightly higher impedance of your Kicker center speaker should reduce the output a little over 3Ω; I don't see any obvious way to adjust this with the controls but it probably won't affect the experience noticeably. The more interesting effect is from the sensitivity numbers. The front door and dash speakers have 88dB sensitivity while the rear doors have 93dB. This means that the front speakers will be putting out 5dB less sound than the rears for the same electrical input, which might be offset by a judicious use of the fader.
It appears that the amplifier output in the MDX is the same for the front doors and pillar tweeters (i.e. no filtering on them). Thus the tweeters can be driven by the front door outputs, instead of the existing tweeter wiring. Some have installed the crossover in the door and run wires from there to the pillars for the tweeters. I chose to not mess with the wiring but instead dis-assembled the crossover into the low-pass coil and the high-pass capacitor for each channel. I soldered the coil in series with the door speaker, and the capacitor in series with the tweeter, before installing. (My center speaker came with a high-pass capacitor which I also used.) In this configuration the door signals are not split between the two speakers as in a crossover, but they are still attenuated as appropriate. Either way (using the crossover and adding wiring to the tweeter or using the components at each speaker) should have the same excellent results.
I doubt that it will be worth it to remove the lining and replace the overhead speakers but that depends on how much you care about the sound for the rear seats. YMMV