Take a look at these. I have not heard them with the HE-6 but I've heard them with speaker. Exceptional. The Odyssey Cyclops is a good place to start - Also the "Stratos". "Gary in MD" in the Speaker amp for headphones thread has one and use it with his LCD-3 - he loves it. That thread has a lot of info in it.
Also - look at the Audio-GD Master-3 /...