To use the EOS 6D raw images with iPhoto you will have to upgrade, sorry, see the Raw Support List:
OS X Lion: Supported digital camera RAW formats
Your camera is supported by Digital Camera RAW Compatibility Update 4.03*; the footnote states clearly: * Aperture version 3.4 or later, or iPhoto version 9.4 or later, is required to install this update.
Your best bet to import the raw images, if you do not want to update, would be to use the software that came with your camera to develop the raw and then to import the converted photos into iPhoto. Usually the camera provided raw conversion is the best, for the manufacturer has the means to provide camera specific functionality.
Regards
Léonie