I tested DACs, preamps all at line level. Didn't provoke me to continue with things like power amps. Now I don't remember it being a 125 tone test signal. I seem to remember something like 12 or 15 tones. I also used wideband noise, with different sections filtered out of the noise to see if any IMD artefacts showed up in the filtered area ( usually filtered out an octave at a time). I used recordings of things with significant output in the 20-40 khz range (jangling keys, cymbals, and such) looking for artefacts at lower frequencies. I digitally generated a few squarewaves with different base frequencies not at even multiples to see what showed up when these were mixed. While the fact it isn't a commonly done measurement would not mean it is of no value, I would think you would see something like this used more often were it to show results that correlate with audible differences regular measurements miss. And that doesn't seem to be the case.