The AS 400 bit must be set in the bin file. It can not be set using SYMCLI or ECC. You will need EMC to set it via a bin file change as far as I know.
Is this a new Celerra? If so EMC² should be involved in the installation of it. If this is an existing Celerra, you will want to make sure that EMC will support booting from CX and accessing storage on DMX. We were told that this is not a support config.