When I use another driver (AppleHDA+HDAEnabler for 10.6.4) i get this one in the same situation:
Kernel Panic (mplayer - CPU3)
Without this driver or just playing a file with digital content it works.
With this driver it seems to work for now:
I was not able to reproduce the KP, so maybe there is some modification in this driver. Could someone check this an fix this driver if needed?