I want a pair of open back headphones to supplement my ATH-M40x's for mixing electronic music. I wanted a second pair with a really wide soundstage and a different sound from the M40s and, after some research, landed on either the K701s or the HE-400is. Whichever pair I get, I'd also like to buy a cheap headphone amp and landed on the E1, but I'm open for suggestions on a different cheap amp. Which pair do you guys think is better?