Hello Phil,

your new motherboard or your distro appears to have reacted to the presence of whole-disk raid members by establishing Gnu Partition Tables on them, blowing away those drives' superblocks.

Yes, this was an unpleasant surprise.  Won't build them this way again.

In particular, knowledge of the filesystem or nested structure (LVM?) present on the array will be needed to identify the real data offsets of the three mangled members.

I don't have the history of original creation, but I'm fairly certain
it was something straightforward like:

  mdadm --create /dev/md0 {parameters}
  sudo mkfs.ext4 /dev/md0
  mount /dev/md0 /mnt/raid5

After the array was corrupted I needed to comment out the mount from
my fstab, which was as follows (confirming ext4):

    /dev/md0                                      /mnt/raid5
   ext4    defaults        0       0

Cheers,
DJ