for those who come after DO NOT SET SataPortMap=0 it will break everything!! haha - to fix fire up a debian VM with the boot VMDK added to it (or use an existing one), lsblk to find it, mount, edit grub.cfg so its NOT 0, save, shutdown and start DSM back up - rather happy i went virtual as its dead easy to revert my bricking DSM!
i set it to 1 and now i get a more reasonable allocation of disks with the first one being the boot disk:
so i'm going to guess i need to set it to 065 (no disks, 6 disk HBA, 5 disk HBA) and when i swap HBAs 0455 (none, 4, 5, 5) - but i'm still not sure if i need to set any other as i'm not skipping ports?