itunes braks my sound settings

Since I upgraded my itunes to 9.2 and 10.6.4 my sound settings have been constantly messing up. From a fresh start after a while the sound would just prevent any signal going from the mac pro to my external usb amplifier. It was working fine before the upgrade. Could it be one of these issues?

USB driver problem with 3rd part usb2 card
USB os/itunes problem

I haven't used any additional audio apps nor changed anything. I have cleared cache's , rebuild permissions and the like.

any help? thanks! 🙂