Yes, you can do it. But its a strain on the memory controller to run 2 sets of memory over 1 to begin with. So you will have to probably set your timings to the higher latency. of course you can test lower timings , just don't be dissapointed with reality. Are those ratings at the same frequency. 1333 memory is usually rated like the 8 set, and sometimes the same set will be rated 9 9 9 24 at 1600.
Thank you all for your feedback. I returned the 9 9 9 24 RAM for another set of the 8 8 8 24 DDR-3 1600 Corsari RAM. As it turns out each three pack works fine on my i7 920, GA-EX58-UD4P MOBO, but can't run all 12 GB at 1600, so I have only been able to run them all at 1333 (at stock CPU speeds). I think I may turn all 6 sticks in for a 12 GB 6 pack. Thought? Have folks had luck running a 12GB 6 pack at 1600 on a Gigabyte GA-EX58-UD4P MOBO?