OK, time to pull up this zombie thread:
Stock HE-500:
* stock pads are average or a bit below quality and sound wise.
* cable is thin silver plate - known by its tendency to be microphonic, and emphasis on the treble which makes ringing in the treble worse.
* back screen is about 65% "full" aka 35% open. My own testing shows that a screen with higher open numbers above 75% open (1/2" ground cloth) is the same as no screen audibly.
* Fuzzor mod. The HE-500 and HE-600 has a lot of magnet surface getting in the way between the membrane and the ear. This causes issues such as reflections and cancellations, Very audible. Less definition in mids and highs. Brighter, edgier, and not a lot of blackness around instruments where there should be some.
* Bass. Even on big watts and high damping, these can get a little sloppy on bass. Tonality very nice, impact good but with added cruft.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Cable: any decent OF copper should do.
Pads: my favorite: MrSpeakers Ether Angled leather - very flat FR, very solid bass. Best of 12 I've tried.
Back Screen off/minimzed. I pack my cans in a ziploc bag when not using them. Sound well more open, and less reflections.
Fuzzor mod: the single most key mod.
Bass: tried blu-tack, sorbothane (effective, glue no good).. best for me was dynamat, cut into 3 strips of different lengths arrayed around the outside edge of the can on that flat edge facing itself the whole way along. Each about 1/2" wide, 1.75, 1.10, .75 inches long for these - spread so gaps are equal. This mod also quiets mid and upper bass issues, and keeps low male voices from getting too bassy.
Fuzzor, pads, back screen: on top of what each promises alone, together: headspace widens dramatically. On some audiophile recordings I get 135 degree wide headspace, almost all in front outside of my head, very rectangular and very much like fine speakers in a prepared room.