John, yes that is pretty much my view of the matter after studying over the years the significance(or non)of more complex factors. Headroom is the power available above the typical 1 watt(not the maximum continuous rating)used at a comfortably loud level. Brief peaks on highly dynamic material such as some classical recordings can be as much as 20dB above the average level, which would therefore require in the neighborhood of 100 watts. A receiver amp which can supply this(at the more meaningful 1% THD level)is entirely sufficient in headroom for this use.
As you indicate, there can be higher power outputs stated for extremely brief periods of time. This was embodied in the previous IHF Dynamic Power rating, which was largely continued in the present EIA/CEA 490-A voluntary
standards (see section 5.1 et seq). Yamaha briefly discusses this in a simplified manner
here . The amp is tested with a 20 millisecond burst followed by a 480 millisecond period down 20dB at the continuous level and then repeated. 20 milliseconds is viewed generally(not totally accepted)as the time involved in music's transient peaks. The power available for the burst(at 1% THD or clipping observed on an oscilloscope)is the rated dynamic power and typically may be on the order of 20% higher than continuous power. For example, my least powerful receiver has a 75 watt continuous rating and a 95 watt dynamic power rating. Not all manufacturers specify a dynamic rating, but it's a valid measurement which can be given a small amount of consideration and may be the closest thing to the number that you're asking about.
