Digital Performer seems to give us the least problems on the Mac. Most DP issues have to do with registration. DP does not see GPO in the instrument list until it is authorized. So the first thing to do is authorize the Player.

• DP failing to recognized the GPO AU component.

USER WORKAROUND submitted by Cal Scott:
"I got the answer from the MOTU DP users group...The solution is to delete the file "AudioUnit Info Cache" and relaunch DP. Then DP re-examines all the AU plugs. And of course, this time is was happy with GPO. It's located: Users/you/Library/Preferences/Digital Performer/AudioUnit Info Cache. Thought this might be useful if one of your other users runs into this dilemma".

(from garritan.com)