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I agree that some of the extra air and resolution probably originate from the elevated treble at around 10 kHz. I also sense that overall we lost some of the hard to point out strength of the Audeze sound, that’s a bit forgiving, full, rich and creamy sound.
I have now changed pads from the leather to the vegans. Changing the pads may not sound like a deal breaker, but I can assure you it can be. I have tried pad rolling on other headphones with the same result. The leather pads reflects more treble than the vegan pads. So the vegan pads tones down the high treble a bit and make the sound more refined.
I have personally preferred the leather pads with earlier revisions of the LCD3 as I sensed a lack in treble energy, but not with my Hifiman HE6 and the new LCD 3 2016 revision.
With the vegan pads on the LCD 3 from 2016 I got the same clean sound, refined treble, black background and resolutions that I got with the stock leather pads. I also and more important got back all, or at least most of the smooth, rich and creamy sound of the earlier LCD3. So with the vegan pads I only lost a little in air, dynamic and bass definition. Well it also clearly toned down the high treble, and it’s a good thing in my book!
Engagement and musicality are as other sound aspect both system dependent and personal. To me the biggest strength the vegan pads has on the LCD3 (2016 revision) is greater engagement and musicality. Take this with some of the added assets the new LCD 3 revision brings to the table; like a bit cleaner sound, more refined treble, blacker background and a bit more resolutions and yes it’s a nice upgrade IMO.