Question. Why is it so important to keep the old HDD that came out of the DMS? Isn't enough to keep the backups?
A "blessed" (original) drive from PhatNoise has a hardware serial number which matches a signature held in an area of the drive outside the PHTSYS / PHTDTA partitions. Even with a full-disk image of the drive, the only place that image can be restored to and still work in an un-patched PhatBox is the same drive it came from.
If you don't care about being able to hack other boxes, you could re-use the original drive for any purpose you want.