On that note... I have had some good time with my HE-560, so I would like to share some impressions...
1) They are highly dependent on amping and also dependent on the amount of current that the amp can push. Less current = bass distortion. And the distortion can get quite ugly.
2) On that note, I have heard them with silky smooth treble out of a solid state amp, and with harsh and hard treble out of a tube amp (Schiit Lyr 2 to the spotlight here), so it's not a general rule of thumb that tubes = smoother treble and solid states = harsher/harder treble for these. I have generally found mine to be far smoother out of solid-state amps that can push a lot of current.
3) Soundstage is also highly dependent on source. Some sources cause the soundstage to collapse completely and then the soundstage is marginally better than the HE-500 at depth, but give them the right amp, and they will give you that big soundstage.
4) Bass is also very highly dependent on sources. I have found that... with certain songs, the current demand from the headphone is way too big, and if the amp cannot cope, there will be either distortion, or less bass in general. Feed them current. A LOT (and by that, I really mean... a LOT more than other orthos except for the HE-6) of that and the bass comes alive. Visceral, weighty, and with very good definition. It's not at all "too tight".
So personally, I am very happy with my HE-560 (thanks to GrizzlyBeast!). But had I not have the opportunity to explore different amp options, I would be stuck thinking this is just another pair of planar magnetic pair of cans that are too subdued to deliver what they can.
Quick comparison against HE-500:
1) HE-560 is obviously less efficient.
2) HE-560 does not sound smoothed over with upper midrange frequencies. HE-500 sounds subdued and sibilant at the same time to my ears. Possibly the lower treble peak at work here.
3) HE-560 has a much deeper and wider soundstage
4) Comfort is undoubtedly better on the HE-560
Quick comparison against LFF Enigmas: (side note: these headphones sound more similar than not)
1) Enigma is darker, and a bit more smoothed over (I wonder if the Focus Pad-A would cause the HE-560 to sound like this)
2) HE-560 is more open, effortless, and has a blacker soundstage. The Enigma exhibits a sort of faint hiss to its soundstage.
3) Both are equal in terms of frequency response as nothing truly stands out.
4) HE-560 is far more comfortable than the Enigma
5) The Enigma is magnitudes more efficient than HE-560
6) Enigma has tighter, quicker bass than HE-560, but yet it sounds thinner at the same time. HE-560 delivers tons of body to everything from bass to vocal.
7) Soundstage is fairly deep and decently wide with Enigma. HE-560 is a bit wider, but also sounds more open due to its design
8) Despite being more efficient, Enigma is still picky with regards to amping. Drive them out of a thin amp and they can get quite thin and lean... with nary any bass at all (Schiit Lyr 2 to the spotlight again). But drive them out of a warm and weighty amp, and they sound pretty decent. HE-560, in light of that, doesn't quite change its sound signature so significantly like that. Instead, it just becomes more docile. Give both headphones the right amp and it's a party.
9) Enigma has a slight tendency to become more sibilant than HE-560
10) Enigma isolates far better than HE-560, being closed-back and at the same time boasting thick ear pads and strong clamping force
11) Neither headphone seems to like bright sources. The Enigma is too sibilant out of a bright source while the HE-560 suffers from treble "white-out" (or excessive treble energy from my perspective)
12) With regards to vocals, I have to give the HE-560 the "edge" here (no pun intended). It is able to present a smoother, less grainy, more defined, dimensional and clean midrange than Enigma. The Enigma has excess warmth that cause vocals to become slightly nasal and quite congested. The midrange on the HE-560 is slightly sweet, and the tonality is just so right. I have been an Audio Technica fan for years, and though I still enjoy a euphoric midrange, the tonality of the HE-560 is so right that I have to hand it to them for being the reference. I surprisingly don't find my Audio Technica headphones "sweet" anymore for the same songs. Yes, vocal is really that much better on the HE-560 to my ears. This is the definitive quality that one can use to distinguish between these 2 headphones.
Overall, I prefer the open design and comfort of the HE-560. I dread their amping requirements, but all in all, I guess I can live with that since I am enjoying the HE-560 so much. It has been a very worthy addition to my collection.