Not wanting to get into too much of his rationale, I haven’t heard it in detail, but wheter it clouds or add slam, It would enhance it, get your focus on it. It’s a bit in the same vein that this new « trick » in production. Since music nowadays has to get trough Iphone speakers that basically don’t reproduce any bass, If you listen all modern basslines have some distortion added to them, so you do hear some more harmonics and it allow to perceive a bass line when really the fundamental is absent on a phone speaker. No it’s not the same but same idea, The extra harmonics will put emphasis on the content.Yup, he definitely puts in that 80Hz bump to enhance "slam". His overall thinking is that low distortion headphones need that in this area as that area is not reinforced by 2nd harmonic distortions that lesser & more distortion prone headphones add harmonics to that area (of course those harmonics are obscuring detail, but they do add to tonality - he's modifying the target curve because he believes the target curve was created with more distortion prone headphones in mind).
EDIT: although thinking about it, 2nd harmonic distortions would "cloud" rather than "slam" drum hits wouldn't they.........I'm just going off his reasoning for including the extra energy at 80Hz, which he said was included due to the low distortion of his drivers. (Maybe it's a win-win: you get the same tonality balanced out, but with the bonus of the defined "slam").