Quote from jerg:
HE500's merits are in terms of tonal balance (I think it has its own organic natural charm, relative to HE560's more neutral / HE6-esque balance), rolled-off treble (HE560 is much airier/extended, and IS less forgiving with music; everything sounds very smoothed-off with HE500), lush reverberant midrange (HE560's midrange is much "quicker" and faster in transients, and in turn less lush for vocal-junkies). All these merits are, as you can tell, preferential.
The stock HE-500 retain a lot of the qualities you have in your modded ones, being a little more forgiving and lusher sounding. I do think the HE-560 is closer to the tonality of the hE-6, and I'm pretty sure that back in October 2013 these were going to be called the HE-6i (for improved).
But I don't want people to mistake your comment about, "everything sounds very smoothed-off with HE500" to mean that the HE-500 tends gloss over details, because that's pretty far from the truth. You know how people tend to read too much into something, and that's a good place for people to misread the intent.