Symphony MK II Pro Tools HD cannot playback core audio outside of Pro Tools and shows 00.00 on the screen

When Symphony is connected to your AVID HD card check if Symphony locks to clock in Pro Tools and audio playback in Pro Tools is working normally.   If so this would be correct.

If Symphony does not lock to clock for playback outside of Pro Tools this is an AVID issue where you need to use the Avid Audio Server app to set the sample rate for core audio playback.

This is located in Applications > Avid > AvidAudioServer.

If you have any issues setting the clock source here open Audio Midi Setup then select the HDX Clock Source here, change this to something else, then back to Internal.  

Then test core audio playback and should be able to adjust the sample rate in Audio Midi Setup normally.