Check everything is set to the advertised specs on the BIOS, then download and run memtest 86+ and make at least 5 passes, if both BIOS and memtest detect 24gb fine and it's stable then it's only a windows-related problem.
Seems it is possible, but most of the time it works with 6 sticks neverthless. Try the memtest thing and check BIOS for 24gb detection.
Worst case scenario( if the sticks are not defective) is you'll have to set them to 1333 instead, but then it'll allow you to set tighter latency, most of those sticks can do 1333 cas 7 without any more voltage, which is actualy faster than 1600 cas 9.
Yes it is quite interesting due to those Intel Specifications it is not recommended to use a 24GB X.M.P. DIMMs and DDR3-1600.
I'm assuming Intel has it's reasons for this particular case. But many individuals outhere who purchased 24GB DDR3 1600 are pretty quick to tweaking the voltage among other things in the BIOS system and surely they are able to achieve the 24GB in the BIOS System and Windows but once again It's NOT Recommended by Intel primarily because in the long term it will damage & decrease the life of many of the components within the motherboard.
I have to agree with you purchasing a 24GB and running these under 1333 is the best thing to do in terms of stability and durability.