Can you confirm that relative colorimetric was selected when you generated the 3D LUT?
Last I recall, there are limited hardware controls on an iMac for changing the aspects of the display. I assume that you simply profiled the display, and skipped calibration. Is this a correct assumption?
That should be the last two questions before figuring out where the warmth is coming from. If you can, try a report on calibrated and uncalibrated and list the reported white point for each.