>...can I cause TSM to use mulitple drives for a direct-to-tape backup/archive?

Fine-grained Collocation choice and MAXNUMMP are the key factors within a
session; and multiple parallel sessions going after subdivisions of file
systems also help (again, watch collocation, to avoid waiting on a single
tape in use by another session).
The Technical Guide redbooks nicely explain the various multi-session
elements.

  Richard Sims, BU