Ok we seem to be going round in circles
If you have a locked hard drive, even with an eeprom backup in c:\backup, and you try and install this hard drive into an xbox with an embedded eeprom bios (rememebr our original motherboard has a corrupt eeprom and needs to be reflashed) you are going to get error 06 every time you boot, this error means the drive cannot be unlocked, which makes sense as our embedded eeprom HDD key is different to the key on the original eeprom (which is corrupt, so we can never recover the HDD key we need)
You can boot with evoX discs or try and FTP all you want, it will never work, you will get error 06 every time you boot.
You need to fit an unlocked HDD and then go about reflashing your corrupt eeprom.
The original HDD cannot be unlocked, as we do not the key, the key is on the original eeprom which has now been reflashed. The drive is now useless, might as well throw it away or return it to the manufacturer
The only way I can see of avoiding this in future is what Lugnut said and to copy the C:\backup folder to a CDR and keep this with the xbox, so if the motherboard dies, we can use the eeprom.bin on our CDR and embed this into a bios, and fit to a new motherboard.
I understand what you are saying about booting from an evoX disc, this is only useful if your original eeprom is available or not corrupt, in this case the original eeprom is NOT available, so I was left with a paperweight 120Gb HDD.