The Audix time is as good as the system (processor & clock) it's running on; may be good, may not be. Bobg1's way is the only way I know of to set the Audix time. There may be an auto sync somewhere, I've just not used it.
Regarding the synching of Definity to PC time, yes via ASA Fault & Performance - Time Synchronization. It does sync to the PC running ASA. Consider the accuracy of the PC & potential fluctuation in its clock with respect to the type of environment your in. If you have A LOT of CMS activity, resetting the clock may skew call stats. Skewing stats isn't too likely unless the PC clock is way off and you're synching many times a day; point is just consider what it is you're trying to accomplish and if it fits into the business environment.