Yes certainly, Mike... But the problem is that there are numerous possible definitions for "dynamic headroom" ratings. When they say "dynamic," how long does the "peak" power or current has to be sustained? - should it last for 1 millisecond or 1 second? - with what level of allowable harmonic distortions? - with how many channels simultaneously driven? - and with what frequency ranges? I have never seen a dynamic headroom spec with all these qualifications.
As far as I know, there is no established industry-standard methods for the measurement of dynamic headroom. This means that there is no way of comparing these numbers in a meaningful manner among different brands. For the same reason, comparing loudspeakers' "frequency response" ratings among different brands is almost meaningless, even if one assumes that all manufacturers publish honest numbers.
There are certain numbers from which you can guestimate the amp's relative power reserve (although it would by no means be quantitative). For example, I understand that H/K publishes what they call "high instantaneous current capability (HCC)." It is certainly nicer to have these numbers than not. But again, without defining what "instantaneous" means, the number conveys little information. Plus, in this case, without having a rating for power-stage's maximum peak-swing voltage, you cannot even start translating the Ampere rating into the actual power delivered to the speaker. For example, H/K's new AVR7200 is said to have an HCC rating of +/- 75 Amperes, which is admirable. But if you do simple calculations, this can imply that the amp is capable of supplying the whopping 45000W of instantaneous peak-to-peak power into an 8-ohm load (75^2 x 8), or 22500W into a 4-ohm load. Of course, this is not at all the case, because the amp's output voltage will clip way before the current limit is reached.
Another rating that I see often cited in higher-end amp specs in relation to dynamic power handling is the total capacitance per channel of power-supply condensers. A $1000-class receiver tend to have 3000-5000 microfarad per channel, while a good separate power amp may boast >20000 microfarad per channel. Again, it is nice to know these numbers, but the capability of an amp's power supply is determined by numerous factors, with the condenser capacitance being only one tiny bit of information.
Obviously, manufacturers regard these specs as powerful marketing tools. Accordingly, they choose to publish only a carefully selected set of ratings, without providing us the whole picture... A huge dilemma for "well-informed" consumers!
Cheers!
