Stop 0x0000007B on Intel US15W with PATA/IDE

Usually when people get STOP 0x0000007B, it's caused by missing AHCI/RAID drivers. I've run into the opposite. My WES7 image boots perfectly from a system with AHCI/RAID, but when I try it on a system with an Intel US15W chipset, which is just Parallel ATA / IDE with no AHCI or RAID in sight, I don't get far.

As far as I understand, the drivers for IDE are always included in the base component. I've had a look in the registry and it looks alright. The ATAPI driver has Start = 0.

I tried running IBW on the target, and that works perfectly. It does look like the BCD's differ from my generalized image to the one created by IBW, but seeing that it works on a system with AHCI it seems that this shouldn't be the issue. I've also checked what drivers IBW adds, and it doesn't include anything I don't already have in my image or add with DISM before applying the image.

What else could be going on here?

Update: Just took my exact same answer file and installed it directly on the target system instead of in a Hyper-V vm. Boots just fine, even after sysprep. So something definitely differs. Any idea where to look? Any docs on what exactly goes on during boot in Windows?