If you've got a library with two drives there is no point in setting up a drive pool, as all that does is combine the two together so that once a backup job has filled the tape in one drive it will move on to the tape in the other drive. Since you have a library you might as well just get the library to change the tape in the first drive and continue that way instead.
The benefit of having two drives in a library is the fact that you can run two backup jobs concurrently, but you cannot run one backup job on two drives at the same time.
So if you want to use both drives, either split the jobs so half are set to run on one drive and half are set to run on the other, or I think if you specify All Drives as the chosen device, each job should just start on which ever drive is currently available.
