Julie :
        HSC (Host Software Component) is the software that controls STK silos, 
and
tells the robot which tape should be mounted on each drive (if you have
different type drives or different tapes), but does not assign tapes to the
requesters.
Normally those extended tapes are defined on a separate pool. What you
should do is define to  your TMS (TLMS, CA-1, ZARA, CONTROL-T,etc.) the
rule for tape assignment and that would do it.
If that doesn't do it, let us know...   Oscar Omar Ortega