Listening impressions:
Highs: The HE6 is quite well-known as having a bright signature, and it can be a bit too much for some people. I'm quite happy to say that the leather pads have made the sound signature warmer. The highs no longer get piercing.
Mids: The same, but now with more emphasis on the lower midrange. All in all I'd say the change is very positive.
Bass: Slightly more impact than the velour pads, but the difference will be quite obvious because of the darker sound signature of the headphone.
Right now it sounds like the perfect accesory for the stock HE6 but there are some drawbacks. One of the most noticable things about the leather pads is that they're thinner than the velours. Because of this, the soundstage becomes even narrower than it was with the velours. It simulates something comparable to a crossfade effect now compared to the old HE6 pads. There's just passable seperation but good depth.
What I like the most about the changes though is that they're so much more comfortable to wear now, unlike the headache inducing grip of the velour pads.
In summary,
Velour: brighter, wider soundstage, less bass impact
Pleather: darker, more bass impact and emphasis, constrained soundstage but more musical and fun sounding
I'll probably switch the pads from time to time since they make the headphone sound so different.
-pad changing guide to follow
