Have been using Pro Tools LE for around 3 years - now v8 (with latest updates) installed on Mac desk top running Leopard and with 4GB RAM plus external data disc for audio files. It has proved a stable platform with all kinds of RTAS plug ins. But Garritan is proving a real problem. I may get away with one instance of Garritan on a single track, but as soon as anything else is added (tracks increased) it promotes the Pro Tools CPU warning message and produces extreme distortion. Increasing buffer size to maximum, helps, but only in a limited way. Add another track, and after a few seconds of playing, the system stops and the Pro Tools waring appears.
As most people have good things to say about GPO, I am completely puzzled at why I am having this problem. Even switching off ambience etc makes little difference.