Ok, here's another AHCI patch to try.
fetch http://apollo.backplane.com/DFlyMisc/ahci08.patch
It is a bit of a long-shot but I'm crossing my fingers. Your AHCI
chipset is running ahci-1.1 and does not have the PMD bit set. It's
possible that the disk identify command is overlapping a page-boundary
and the AHCI chip is blowing up the machine when that occurs.
I'm a bit at a loss as the problem appears to be a bit
non-deterministic.
-Matt