David,

Two options that I see:

1)  Point the copy pool device to the 3590, then use the copy command to
copy a 3490 copypool volume to the same stgpool.  ADSM will read the data
from the primary pool tapes.
2)  Create a new copy pool pointing to the 3590s, then do a backup stg from
the reclaim pool to the new copy pool.  You can then 'discard data' on the
3490 copypool tapes. (I think).

Doug Agnew