I am returning to hi fi after many years (kids finally out of the house and I actually have some money at the end of the month!)and trying to sort out fact from fiction. The next item I plan to upgrade is my amp.

Once you move past circuit city type products there seems to be a huge difference in amplifier brand and model prices. Is there any empirical, double-blind study, NRC research, etc. evidence that support these differences, outside of WPC and power supply?