Originally Posted by optiontrader

Agree at looking a little too hard at the specs. SNR, as you may know, is a ratio between strength of a reference signal (like a sine wave) versus measured noise; or a simple difference between the two in dB. Recall dB is logarithmic (similar to the concept that to increase power by 3dB, you need to double power), so 92dB represents a HUGE difference between signal (music) and noise, almost to the point of being negligible.

THD is measured the same, but it can be "tricked" depending on how the manufacturer rates their amps. THD increases as the amp's power increases, until it clips; that's where THD spikes up. Most manufacturers rate the power at that clipping point (usually 1% THD), so you'll usually see that spec.

However, some manufacturers under rate their amps (like RF) - it still clips to 1% at the maximum power (say 150W for a rated 100W amp). But since you're taking the THD measurement at rated power, it's much lower (like 0.05% to 0.1%).

Practically speaking, you'll only hear this when you're over-driving the amp, and you'll only notice at what power it starts to clip. Within it's power envelope, however, you won't hear the difference between an amp that has 0.05% THD to one that has 0.1% THD.

Any of the high-end amps will deliver excellent sound. So look for the amp that has the power and features you need. But most important, as bigaudiofanatic has said, once you get the amp, installation quality is what should be focused on.