[Park Seward]

See if this helps any:

"When you have finally exceeded the limits of your CPU, an error message stating "You're running out of CPU power. Take out some plug-ins to free up CPU power (-9128)" will appear onscreen. From this point, it will be necessary to de-instantiate one or more of the plug-ins to achieve playback. To squeeze the highest RTAS plug-in count out of your system, you must manage your CPU resources wisely. Here are a few recommendations for optimizing your CPU usage:

1) From the Pro Tools menu choose Setups > Hardware. Set the CPU Usage to 75 or 85%. This setting determines the percentage of CPU processing the software will be able to use from your system's total
CPU resources.

2) When you have completed tracking in your Pro-Tools LE session and are ready to mix, choose Setups > Hardware and set the Hardware Buffer size to 1024. This may allow instantiating of one or more additional RTAS plug-ins as compared to the lower Hardware Buffer settings. You can experiment with this setting to see how it affects plug-in performance.

3) The RTAS D-Verb plug-in is the most CPU intensive of the RTAS DigiRack plug-ins. Most high end systems will max out at 4-5 RTAS D-Verb instantiations therefore it is not practical to instantiate a separate D-Verb on every track. A more appropriate alternative would be to create a Stereo Auxillary track with the RTAS D-Verb instantiated, and then bus any audio tracks that require effecting to this track. You can apply this method to other RTAS plug-ins as well. The goal is to share one RTAS instantiating between tracks that require similar effecting.

4) Keep in mind that the amount of automation and the number of edits in your session will directly affect the amount of RTAS plug-ins available. Conservation in one area will free up more CPU resources for another. Having unnecessary applications running in the background can also lower the amount of available RTAS plug-ins.

5) Remember that Audiosuite plug-ins do not require any CPU resources. Most RTAS plug-ins have an Audiosuite counterpart which makes Audiosuite processing practical when CPU resources are running low. Since most plug-in settings are savable as well as interchangeable between RTAS and Audiosuite architectures, a track instantiated with an RTAS plug-in setting will sound similar to the same waveform processed with it's Audiosuite counterpart."

Also:

"Maximum Performance Guidelines

Recording to the system startup drive is not recommended or supported
Although limited recording and playback of audio tracks may be possible using the internal startup drive, a separate external dedicated audio hard drive (or multiple drives) is highly recommended for maximum performance and track count."

Also, run the 10.4.9 COMBO updater.

Hope it helps.