Just recieved my HE-5 from Currawong, and here are my initial impression.
Sound
Compared to my now gone HF-2, they definitely have a much more laid back characteristic, on the borderline of sounding dark. Yet, on the otherhand, I do detect a hint of sibilance that has been talked about to death. However, I think this might be an issue with amplification.
Using my Purity Audio Caliente, which had no issues driving high impedance headphones such as the AKG K501 (which would usually be listenable at levels around 1:30-2:00 on the knob), I assumed that the Caliente would have enough juice to power the HE-5. I'm finding that these cans are VERY demanding, as the Caliente can keep up but barely.
Using my reference test track Def Bass Krew by Dr. Crankenstein ("Officially Sanctioned SPL Competition Disc"), which essentially was designed to test subwoofers in cars, I can usually test how much a headphone can handle, but in this case, it was more like how much my amp could handle until the bass began to clip. With my now gone K501, I could have easily pushed it to 3 o'clock before it clipped, but by then, it would have been at levels that are unlistenable with normal music. With the HE-5, I'm able to push them to around 1-2o'clock, anything after that the bass clips like mad. There is however, definitely a lot of sub-bass packed in the headphone.
With normal music being played, driving the amp beyond 1-2o'clock makes the treble exceptionally bright and fatiguing. Oddly enough I actually enjoy low-volume level listening with the HE-5 (maybe because of the peaky treble emphasis when it gets to normal listening levels?), which was actually the same level of amplification that I had running my HF-2 at normal listening levels (around 11 o clock).
While I've been contemplating getting a new amp for a while, I think the HE-5 might give me a legitimate reason to upgrade.
Just an FYI, my initial impressions generally point out flaws of headphones rather than strengths. I'll definitely post more updates when I get used to it's sound signature and see if more burn-in affects the sound.
In terms of build/comfort, it's like a hybrid Grado/AKG - on the one hand you have what feels like a waist belt wrapped around your the top of head, and then you have the plush cups very similiar to Beyer/AKG. Overall, while it feels hefty on your hands, its more evenly distributed on the head.