Sorry to hear about the issues you have with your sample.
I my case the Mute function works as it is supposed to - it silences the Diablo completely.
Regarding freezing after standby I rarely power mine down (fully or partially). But when I've done so I have never experienced any problems.
I...
I lived with the Diablo 300 for 7 years when I got an opportunity to evaluate the 333 with my Sonus Faber Amati Futuras.
And the new devil was a different beast.
The 300 is richer, darker and some what grainy when you push it.
The 333 has more air, wider presentation and much faster dynamics...