>>We walk this way.

Backup Storage Pools (Criticals)
Backup TSM Db
Backup Storage Pools (non-Criticals)
Expiration
Move drmedia
Run Drm Prepare
DR preparation and mksysb on TSM server to tape
Take tapes to Data Vault.<<

I would highly recommend moving your DRM PREPARE to immediately after your DB 
backup.  In a DR situation, you will only be able to recover to the point of 
your DB backup.  You won't be able to recover the current days non-criticals 
since they aren't refected in the DB backup.  The expiration may resulting in 
emptying tapes that you will be using in the DR situation since they still 
contained data at the point of the DB backup.

I see no benefit in delaying move drmedia until after expiration.

David Ehresman