Devialet Expert isn't good in showing secondary harmonics?

[ogs]

If your cable designer meant second harmonic distortion then the only measurement we have as far as I know is from the Stereophile test of D-Premier: http://cdn.stereophile.com/images/113Devifig08.jpg Here the second harmonic distortion component is just a little lower in level than the third. The general distortion level is very low.
In a normal single ended tube amp you'd have fairly strong second, fourth etc harmonics while third, fifth etc would be lower in level. Damon's reference to 'bloom' is a good description of the typical tube sound. The same could more or less be true for a class A transistor design. An old theory I've heard is that an amplifier stage should have a distortion signature with second harmonic a little stronger than third, then fourth, fifth, sixth etc with decreasing level. Modern amps (not just Devialet) tend to have more odd order harmonic distortion than even.
The statement you refer to is fairly non-technical and a bit strange...