Prommi MkII controller doesn't support booting colder than -40 degrees. -40 is as cold as the boot temp can be set at. The GT controller is different, hence the software and firmwares for em say "for GT only".
If you want colder you need 2x PSUs. Wire the prommi to one PSU, and the PC to the other, so that the prommi no longer has control over the PC.... leaving you free to switch it on at whatever temp you wanna switch it on at, however this will also remove all safeguards that the controller offers.
