Be careful with dynamic power specs. A good spec, which by the way I've never found, ought to read something like "300W into two, 8 Ohm loads for 100 msec with 25% duty cycle from 20Hz to 20KHz with no more than 1% THD+N". Just look at how complete that spec is.
The reason the 100 works and the M5 barely does with the ADA example I gave is the higher sensitivity of the M100. The M100 can hit at least 4 dB higher than the M5 with the same power level.
Now you could power the M5 with a 1250 or 1500 but you start to run into design limits of the M5. At that point, you are better off going with an M60 or greater.
Note too that my FWB powers her M5s in her very large living room with my 20 year old, 90W Denon. No sub. No problem. For most, the ADA-1000-2 would likely be more than enough.
You can't wave away the extra 10% difference in capacitance without being intimately familiar with the design's performance. Perhaps the AC ripple was too much and it was messing with the noise margin. Perhaps the design was meeting the peak spec but the duration wasn't long enough causing smearing of instruments. You just don't know.
