RMS and peak watt output differ by Dynamic Headroom. For example, a 100w RMS rated amp will be 100w = 20 dBw (dBw = decibels above one watt) at full continuous output (give or take). This means that if you have speakers rated at 90 dB, with this amp, they will produce 110 dB in theory. If the amp has a dynamic headroom of +5.7 dB, it can produce 370w in short term bursts. (+3 dB would equal 200w output, +6 would be 400w and so on) Very few amps even list their headroom anymore, mostly because of consumers who think a 110w amp is much better than a 90w one. They rate them and design them to have big RMS power to look good in ads or store salesperson lingo, but they have 1 dB of headroom in most cases, pretty pathetic IMHO.
Good equipment (like NAD built in the early 90's) had balls. You could buy an amp rated at 60w RMS that could put out 200w into 8 ohms, and 330w/ch into low impedence loads (+5.5 dB of headroom).
The NAD 2600A in my sig is rated at 150w/ch into 8 ohms, but is rated at 400w peak into 8 ohms in stereo (+4.3 dB), and is also rated at 1600w into 4 ohms mono. That's an amp!
