Win7U X64 crashes on setup reboot

We have a new build for a friend's Media Center, and for the first time ever with Win7, I am having an issue with the installation that I can not isolate.

The System:
AMD Phenom II X4 955
Gigabyte 8900GPA-UD3H
2 x Kingston HyperX Blu 4GB (2 x 2GB) DDR3 1600 (KHX1600C9D3B1K2/4GX)
4x Seagate 1.5GB SATAII ST31500341AS (in RAID 5)
LITE-ON SATA CD/DVD Burner (iHAS124-04)
Windows 7 Ultimate SP1 X64

We tried installing to multiple system drives, and they all end up completing the installation, rebooting, but reboot just as the flag starts to cycle in. no BSOD, no error messages, just reboots every time. Safe mode gets as far as achix64s.sys, (which leads us to think some kind of drive/er or controller issue) then reboots.

We have tried:
setting the BIOS to all available combinations of RAID, AHCI, and IDE modes
Updated drivers (even though win7 has recognized all the drives right off)
isolated all the memory sticks 1 by 1
different cables, drives, and PSU
swapped the mouse pad, just in case...

We also each went over it separately to eliminate potential PEBKAC, but each got the same results.

I desperately want to beat him about the head for trying to save $110 by going AMD instead of Intel, but to be fair I have to inquire of those that may be more knowledgeable regarding AMD installation issues...