I just wanted to share my experience with a terrifying part of the upgrade, because I couldn't find solid answers for this level of hardware anywhere.
Due to some hardware failures (old motherboard dying a slow death) I needed to upgrade my Rampage IV Formula and went to a Maximus IX Code.
I was terrified I was going to lose the data on my ~11TB raid array (4x4tb in a raid 5). I spent a few days backing up all the important stuff to every other bit of media and stuff I could find. I had about 5TB of media that I thought I might just lose because I wasn't sure what to expect. I don't want to debate the merits of firmware raid 5, I know there's a lot of opinions but this is the perfect solution for me, and has seen me through two disk failures unscathed.
On the old X79 board, there were 4 3G SATA slots. These were all full with the disks making the array. My OS and Fast data disk were on an as media controller that was present. The Code has 6 sata ports all driven by the 270 chipset. I put my OS and Fast data disk on ports 1/2, and moved the raid disks to 3,4,5,6 -- keeping them in the same order that they were on the old system. I set the BIOS mode to proper raid, and then the box rebooted, and the raid BIOS picked up the volume as well as all the disks in the right order.
It even persisted a user error, one of the disks didn't have the power cable properly seated, so it kept spinning down and ultimately got reported as failing by the array. The array was marked as degraded, and the it kept trying to rebuild the array. I noticed the windows logs that it kept issuing resets to the volume, and then the disk finally vanished completely. I powered the system down, checked my connections and found the issue. The system came back up, recognized the disk, put it back into the array and started a rebuild. As I post this the data is all accessible, and the rebuild is nearly 50% complete (it never went past 2 w/o the errors before).
I'm very pleased to report that the firmware raid survived a nearly four year leap in chip sets. Thanks to Asus & Intel for this one.