I hate to be the bearer of bad news, but you bought 2x 12gb kits, so they most likely won't be able to run at the rated speed as those rating apply only to one kit. I've never built with that much RAM, but I would speculate that if you loosen up the timings to 10-11-10 you might be able to get it stable at 1600.
K taking guesses, you mean Rampage 3 formula? 1366 socket and 6x 4GB cause they do not come in 6GB dimms.
If that's right, what have you tried so far? Try enabling XMP and taking down the RAM speed to maybe 1066 and work your way up and see if that works. You may just not be able to run that set at the full 1600Mhz.
My problem I've figured out is that it's not ALWAYS recognizing the 24GB. I can be in the BIOS and it will recognize 24GB at 1600Mhz, then restart and go into the BIOS and not its only 16GB. I've now heard that the whole i7 9xx series is having problems like this.
I've tried exactly what you said and it happens just the same.. once in a great while it will decide to see all 24GB. It's too late to take my RAM back to get a set that is on the QVL.. not that it would even matter.