200 Peak Watts @ 4 ohms vs 75 rms Watts at 0.1% THD at any frequency from 20 Hz to 20kHz @ 8 ohms. Which is the more powerful amp?
RMS watts mean root mean squared watts. It is also call continuous watts. It is the average of the power output in the form of a sine wave (the shape of analog sound). Peak power is measured at the very peak (top) of the sine wave. It is an instantaneous, maximum measurement. RMS is the average or continuous power output (roughly 70% of peak).
A amp typically puts out more power (close to twice) at lower impedance (4 ohms vs 8 ohms). Always compare AVRs/amps at the same impedance rating. Lower impedance (2 or 4 ohms) enable the AVR/amp to produce more watts but also more heat and some AVRs are not stable with low impedance speakers.
Picture it this way:
Peak or Dynamic watts at 4 ohms are like driving your car DOWN a hill on a long, straight road. Man, can you go fast and it does not really require that much power. But if you go for a long time like this, the engine may over rev and throw a rod.
RMS watts are like driving your car UP that long, straight road. Not so fast anymore. The engine has to work much harder. You need more power to go as fast as you went downhill with less power.
RMS watts, rated from 20Hz to 20kHz, at .1% Total Harmonic Distortion (THD), with 2 channels driven into 8 ohms is like driving your car up that hill with your family and all their luggage loaded in it. Not very fast at all unless you have a big, powerful engine. This is a much truer test of the power of your engine. Most of the good, mid priced AVR are rated this way. Like Onkyo, Denon, Yamaha, etc.
RMS watts, rated from 20Hz to 20kHz at .1% THD, with ALL channels driven (5 or 7) into 8 ohms is like driving up that hill with your family and all their luggage while TOWING your boat. If you want to get up this hill with this load, you need plenty of REAL power (watts). This is how good separate amps are typically rated.