Default [Q] Converted to GPE, difficulty converting back. Help?

Converted an M7ATT to GPE - the owner wants it back to stock. I don't know how (probably an OTA) but S-ON got re-enabled and bootloader is locked. I tried unlocking it via HTCDev but it won't take.

-AT&T M7
-GPE fastboot/bootloader
-GPE Recovery
-Bootlooping as soon as it hits Android
-S-On / Locked(tampered) bootloader

When I try an RUU exe, it just says device not found. When I try it via rom.zip / commandline, it just says FAILED (status read failed (Too many links)).

Any suggestions?