[DigiTechSupt]

Which softsynths are you seeing the problems with? Which ones do you have installed and what are their version numbers?

I'm running things just find on a Mac Pro 2.66, including NI synths, Hybrid, Stylus, etc.

One thing to try:

Go to MacHD>Users>your account>Library>Preferences>By Host and trash 'com.apple.midi.a bunch of numbers and letters.plist'.

Go to MacHD>Users>your account>Library>Preferences and trash 'com.apple.audio.audiomidisetup.plist'.

Empty the trash and restart, then see if everything is working.