Well,

Doing the backup to disk and then using Vault is about
the only way to be able to accomplish what you want to
do. By the way, you are correct about the backup only
going as fast(slow) as the slowest device. So the
backups, even though one of them is going to disk,
would slow down to the speed of the backup to the tape
drive. It is one of the reasons they don't recommend
doing inline tape copy to disk and tape.

Jeff

"A wise man once said 'Wherever you go, there you are'"
      -Mike Brady