I am not sure about the 12"ers but on paper the Omegapro 15" driver has a considerably flatter response to 1000Hz than the Kilomax 15" driver. The Kilomax has a pretty nasty dip that starts at 500Hz.I love the Stage 4 Pis , no puny 6" midrange speaker could ever hope to deliver what these speakers bring to my ears.
I recently picked up a Parasound HCA-2003 to power them and the combination is unreal. The speakers have litterally brought tears to my eyes with their lovely sound.
http://editweb.iglou.com/eminence/eminence/media/speakpro02/graphs/om15.gif
http://editweb.iglou.com/eminence/eminence/media/speakpro02/graphs/k15.gif