I own a pair of those, they're decent phones but a bit too neutral in my opinion, so I had to use EQ to make the sound more desireable to my tastes. Here's the EQ I use for my X2s, but it's similar to the one I used for the DT880s. http://i.imgur.com/R7wdh4i.png
It's quite distorted and I've been laughed at on audiophile forums, but I enjoy a bit of flavorful sound. On to the topic of amps, do the more fancy ones make any noticeable differences?
I actually prefer headphones to be neutral, so I can use my own EQ. That's why I want the M40's instead of the M50's.