Got my HE-6 today
I haven't done much A/B'ing with the HE-5LE though. One reason is that the sensitivity is quite different, so it's very hard to make sure they are at the same volume.
That said, the HE-6 are sounding great on their own. One of the things I seem to notice is that the bass seems even better than on the HE-5LE. Also, the HE-6's lower sensitivity makes them less prone to the subtle hiss/noise I can hear out of my Pioneer A-35R speaker amp on the HE-5LE. The amp is rated at 45 watts per channel RMS into 8 ohms and 65 watts per channel into 4 ohms, and I get a nicely loud, balanced sound with the HE-6 right around 9 o'clock on the volume dial. I'm running them off of the speaker taps with an XLR-to-bare-wire adapter I bought from a great DIY'er (email@example.com).
I don't have a very stable "repertoire" of songs I listen to, so it's hard to give responsible impressions without taking the time to do careful A/B'ing. Maybe someday... ;)
The build quality feels very nice, with everything being a bit stiffer (i.e. less loose in a good way). The hinge that holds the cups certainly feels sturdier and has less "play". I did notice a couple of imperfections on the metal rings that hold the cups, but it's nothing I would bother to return them for.
As others mentioned, the metallic finish on the cups is reminiscent of the Ultrasone Edition 9. That said, they don't seem to pick up fingerprints nearly as much as my Edition 9's used to. I hope that their finish is more resistant to flaking/chipping off than that of the Edition 9.
The headband is a bit thicker, so the cans fit my head better. The HE-5LE were *a bit* loose on my small-ish head even on the shortest position, and the HE-5 even more so. The headband's material is better than on the HE-5LE, feeling more like leather than vinyl. It also wraps around all the way, whereas the HE-5LE only has it on the top.
The inside of the HE-6's cups is a bit more complex than on the HE-5LE. There is a quarter-circle of foam behind the cloth, together with a metallic ridge that runs across their diameter.
The cable looks very cool and it's extremely flexible and non-microphonic.
As I have written this post, I have listened to a few more songs and the general impression I get is one of great clarity coupled with deep, satisfying bass. So far, no regrets! Based on memory (which is a *very* tricky thing to rely on in audio), I would say that they take the HE-5's sparkling highs and combine them with the HE-6's non-fatiguing nature and deeper bass. Do keep in mind that I sold my HE-5 months ago and I have only listened to the HE-6 for a couple hours.
I'll let you know if I get another audiophilic epiphany ;) 1:35AM, time to go to bed...