I've done some more listening with the A2 and my HE-400s and yea, I'm not sure there's enough of a difference in sound to justify me keeping it around. It sounds great and if I didn't already have the E17 around, I would probably keep it. As it stands though, I can get the HE-400s sounding good enough (to my ears) without spending that much extra cash.
Mine also hums and it's pretty dang audible, even near my buzz-happy plasma TV. I can hear it from my sitting position which is probably about 8' away. Obviously it's not noticeable while I'm actively using the headphones. I probably wouldn't have even given it much thought if not for good ol' Head-Fi ;)