The first thing that struck me about the 356 was the superior bass control. At higher volumes the sound remains clear when the 326 starts to get congested. I haven't had the 326 for about 2 months now so I can't add too much to what I said, but the bass accuracy was better.
That said, 50 watts to 80 watts isn't a huge amount of change. There are integrated amps by Arcam, Nait or Rega where a 70 or 80 watt amp may have more control at higher volumes. My Parasound A21 P7 combo is clearly superior to the Nad 356, so I guess I'm saying, don't expect jaw dropping improvements. If you can get the 356 at less than retail, or used, it would be a better option.
That said, 50 watts to 80 watts isn't a huge amount of change. There are integrated amps by Arcam, Nait or Rega where a 70 or 80 watt amp may have more control at higher volumes. My Parasound A21 P7 combo is clearly superior to the Nad 356, so I guess I'm saying, don't expect jaw dropping improvements. If you can get the 356 at less than retail, or used, it would be a better option.