Thanks, all.
I had a chance to try out both models this evening. And, the YouTube videos didn't lie: I much prefer the AP sounds on the MX88. The action was slightly more responsive on the CK (I always use "Doctor Gradus ad Parnassum" from Debussy's Children's Corner to test this), but the MX was more fun and inspiring to play in general, for some reason. So, it looks like the MX88 is the keyboard for me (at least for the time being).
BTW, I also tried out the P125, and the AP sound quality was comparable to the MX88. Also, the action was fantastic on the P125, even better than the CK!