Designating audition outputs has changed in Digital Performer 3. Previously, DP's hardware driver's "Monitor Outputs" determined where auditioned soundbites, scrubbing, etc. would be assinged. DP3 now uses the Audio Bundles window to determine ouputs for auditioning.
Clicking on the OUTPUT tab in the Audio Bundles window will display all output bundles. The output bundle which is at the TOP of the list will always be the audition output as well. You can change which bunle is at the top by using the "MV" (move) buttons to the left of each bundle. Simply drag the desired bundle to the top of the list. Then he output of that bundle will be your "audition" output.