This thread's been all over the place, no offense... There's a difference between portable and transportable IMO.
The Beyers and MD are transportable, i.e. reasonably rugged so as not to get destroyed in a bag even without a case; but I'm not sure they're something you'd be comfortable wearing around your neck for more than a a few min and they're gonna fill up half a backpack...
Don't get me wrong, I love my DT 880 and I find them incredibly comfortable to actually wear. They're open tho, forget that semi-open nonsense, you're right to steer away from them for portable use... Whomever called them closed on the 1st page can't have ever used them. The Beyers are relatively compact for full size headphones so if you're after a transportable setup the 770 are a good value. I'm actually looking at the Mad Dogs myself for living room use, for the sound signature they seem to deliver as well as the isolation factor...
Not quite sure if the MD are any more compact than Beyers (doubt it), but I'm not sure I'd ever travel with either anyway. Maybe if it's a long trip or whatever and I'm mainly using them in a hotel or wherever I'm staying...
For portable on the go use, walking around town or short trips etc I'm much more at ease with something like my V-Moda M-80 (or something like the UE600 or Momentum, tho the latter are larger), they're much smaller than you'd think from looking at pictures. I can slip them into a messenger bag next to a laptop and still have plenty of room for other crap, no real need for an amp, perfect degree of isolation vs awareness for me, very durable, can leave them around my neck if talking with someone, great overall package tbh.
Completely different category and class of headphones tho. If you find on-ears uncomfortable or you want something that's more transportable then the MD seem like a strong value, can't wait to try them myself. You could try the M-80 at any Radio Shack or Microsoft store. You could try the Momentum at Apple stores or Magnolia Best Buys, you could try the UE6000 at any Best Buy. Guitar Center should have the DT 770, and finally Dan has a pretty good return policy on the MD. You can find the M-80 online for as little as $150...
I'd recommend at least taking a look at some of the more portable alternatives to see if you really wanna go with full size circumaurals or whether you'd be satisfied with something lighter even if it's a step down.