Uh.......DHWilkin "Dynamic range" has to do with the range between the softest and loudest sounds which can be recorded on a particular format, or which are present on a particular recording. It has NOTHING to do with frequency range.
And NO signal can exercise cones more than broadband noise, as (unlike music) it has sound present at ALL frequencies simultaneously. Since your diaphram IS reproducing the highest frequencies within the passband (defined in digital recording by the sample rate), then it IS reproducing "transients" to the limits of the digital format. By the way...high frequency response and "transient" response are different ways of expressing exactly the same thing...the ability to respond quickly to high frequency waveforms. By their nature, all true "transients" are high frequencies, since low frequencies are by nature "slower" (the lower the frequency, the "slower" the diaphram movement. This is NOT the same thing as saying that the speed of sound is different at different frequencies! Only an expression that, for example, a diaphram reproducing a 40000hz sine wave is moving 100 times faster than one reproducing a 40hz sine wave). A device which can reproduce extremely high frequencies cleanly by nature has "fast transient response". One which can't, doesn't!
As for "dynamic range" being important in "breaking in" as opposed to music, consider this. SOFT SOUNDS by their nature require very little of a diaphram! They're NOT "exercising" it to anywhere near it's limits. So if "breaking in" is real, and exercising the diaphram is the goal, then soft sounds would seem to contribute precious little, right? "PUMP UP THE VOLUME!" If you accept the above, then dynamic range of source material would actually seem to be detrimental to "breaking in" diaphrams, right? I mean, during much of the "duty cycle" the diaphram is doing nothing, or almost nothing during "quiet passages". Wasted time, it would seem to me! As for my second point, since when reproducing noise the diaphram is moving back and forth from near it's limits of forward motion, to near it's limits of backward motion, THROUGH the "zero" position (or center resting point) each cycle, then isn't it doing everything required for "dynamic range" while reproducing the steady state noise? Each cycle the diaphram passes from one extreme to the other, passing through the zero or "rest" position twice per cycle.
See, I told you that an argument could be made that noise is a BETTER source for "breaking in" (if breaking in is even necessary) than music. And I just made it (the argument)!