So Massdrop makes their own HD6XX.
Often times, Massdrop makes their own little adjustments to these custom designs. They've done it with things like the K7XX to great success.
So, there's a mod to the HD650 known to improve the sound (to the ears of most) called the KISS Mod: http://www.superbestaudiofriends.org/index.php?threads/hd650-kiss-mod.3440/
Do you think Massdrop could add this mod preinstalled to the HD6XX?
Maybe we could call it the HD650+, HD6XX+, or HD6XX SE (second edition, or special edition) or something.