Digital Performer doesn't need much extra RAM. Typically, The only time you need to assign more RAM to Digital Performer , would be if you are using 3rd Party Plugins , such as Waves, AutoTune.., or software synthesizers, like Unity, Reaktor...etc.
The main reason DP doesn't need much more RAM, is that MOTU Audio System is responsible for doing the "heavy lifting" for DP. MAS uses Dynamic Ram Allocation. This means it takes what it needs from the "Finder". So you won't have to allocate more RAM to the MOTU Audio system ... it allocates on it's own.
After all of your programs are launched and running , go to the finder and under the Apple Menu , you will see "About this Computer". Here ,look at the "Largest Unused Block". This is how much RAM Digital Performer has to work with. The more Ram available here , the better performance you will get with Digital Performer.

Here's how to change DP3's RAM allocation.

1.Quit ALL Programs that are running (including Digital Performer).

2.In Mac HD, find the Digital Performer folder and open it.

3.Click ONE time on the Digital Performer application icon , which will highlight it.

4.With the Digital Performer icon highlighted, go under the "File" menu in the top left corner of the apple menu and choose "Get Info"

5.Click on "General Information" , and change it to "Memory"

6.Here you will see a "Minimum" and a "Preferred Size" field. Never alter the Minimum size field.

7. We've found that DP3.02 works pretty well with 100-150 megs allocated to its Preffered size. This depends on the amount of 3rd party plugins you have, and how much available RAM your system has.

Example: If your current Preferred size field says "59724" , change it to "79724".

8.Now just close the Memory Info box by clicking in the top Left corner.

9.The next time you launch Digital Performer it will have more RAM to use.