I've run the CX9s w/ Velocity A23 rims, no problems at all. Only concession was to swap the two spacers around so that the thinner spacer was between the pad and the arm of the brake and the thicker spacer was between the arm and the nut, just the opposite of how they came out of the box. Had to do the same thing with Avid Ultimates, BTW.
Thanks for the advice Scott. Had to do the same with my current low profile canti's to work with major tom's.
I can confirm CX8.4s w/A23s with no problems as well. I didn't move any spacers...they are as they were straight out of the box.