Small info for fellow x79 users:
You all know that Intel had to make a chipset revision because of 6G problems and it seems 10 years later the problem shows it's head:
about two weeks ago, one of the disks connected to Intel 6G port started disconnecting randomly.
I've disabled Intel SATA controller and used ASMedia 1061 for 6G connectivity.
About a week ago I've started getting "Machine exception check" BSOD (when lucky) when scanning hardware.
System worked completely normally until I scanned for hardware changes or tried to install new drivers for anything - from GPU to G13 keyboard.
So I've swapped from 1680V2 to 2667V2 and no change. Then to 3930k - same deal ...
Then I tested RAM sticks one by one, then PSU, GPU, completely disassembling the board, washing it, new pads, etc...
After days of hair pulling I tried to search for a new motherboard, but, OMG, people around here are asking 200 euros for x79 MB
Anyway, as last desperate thing, I've disconnected disks and voila - everything worked! Then I connected them to 3G ports and again - everything worked!
So it looks like external 6G SATA controller isn't connected by PCIe bus but somehow goes through Intel 6G controller and if that one fails, external will cause problems as well.
Hope it helps someone to save their hairline ...