I use HD650s and don't find them dark with anything, save my (departed) Woo WA6 tube amp.
I use them with the E7, E17, and Arrow, all set flat, and find them fine.
Of course, I have a couple of minor mods: Cardas Clear Light cables, and removed the foam.
(For reference, I like flat (not boosted) or slightly soft treble, neutral to slightly warm midrange (voice), and flat to slightly warm bass.)
Can someone point me to the E12 review(s)?