@nmmmusicman, The Vandersteen Quatro's are a very different speaker load than the Thiel CS 2.3'.:
Vandersteen Audio Quatro loudspeaker Measurements | Stereophile.com
Unlike the Vandy Quatro's the CS 2.3's don't come with a built in 250 Watt amp to take care of the heavy lifting. The CS 2.3's are recommended to be used with a minimum of 100 Watts per channel of amplification. The CS 2.3's impedance dips to 2 ohms, stays below 4 Ohms for most of the time, and has a high capacitive phase angle. The Vandersteen Quatro's briefly dip to 7.6 Ohms, stays above 8 Ohms the complete rest of the time, and has a low electrical phase angle. The Aleph 3 can't double down it's 30 Watts per channel into 8 Ohms down into the 120 Watts into 2 Ohms asked of it with the corresponding reduction in sensitivity into the 2 Ohm load of the Thiel CS.2.3's. Stereophile (probably as an act of mercy) only tested the Aleph 3 into a 2 Ohm load into 1 channel where it barely increased it's 30 Watt 8 Ohm rating to 39.1 Watts. Keep in mind that the minimum power recommendation for the CS 2.3's would have been the equivalent of 400 Watts into 2 Ohms. These speakers present very different loads to an amplifier.
I'm not sure where your quote comes from, but when one describes an amplifier as being stable into a given load; all they are saying is that the amplifier won't go into oscillations at that load, not how much power it produces, how it sounds doings so, or what levels of distortion it resorts to in order to comply with that criterion.
Yes, "Not everything can be derived from measurements....", but some measurements can reliably provide, consistently predictive results.
