I just got a FiiO E10 with my HiFiMAN HE-400's and it performs quite well with movies. My headphones are open as are the AD700 headphones which does mean that bass can occasionally be less than closed cans. The E10 also has a bass boost knob which does help. I am not sure if the E7 has this feature.
I have also heard good things about the Asus xonar but can't comment since I haven't tried it. The Xonar is only a sound card and does not feature an amp though. I dont know if the Ad700's are easy to drive but that is also something to consider. Do you have a budget? The Astro Mixamp can do virtual surround and runs about $130. Plus you can use it with a PS3/4 or Xbox 360/One.
Hope this helped.