The comparison isn't really fair because the DT880 is beyer's flagship open model, whereas
the 770 is their closed model. I'd be interested to know how the 990 compares because SOS
listed it in their recent headphone article and yet have never reviewed it.
It's confusing because the model numbers suggest that 990 is 'best' and yet the 880 is
the higher priced model (and seems to be equivalent to Sennheiser's HD600). Also, though
the 880 is 'semi-open', to all intents and purposes it's a fully open headphone that
offers very limited isolation.
When I compared it with the HD600 it had a
brighter top end, which was kind of airy but also a bit sibilant (interestingly in a way
that reminds me of beyer's MC740 mic). The low end was as impressive as the 600's though
I tried the hi-fi 'edition' model that seemed to buzz on low notes so I rejected it.
Interestingly I've recently begun to find my 600 a little wooly in the bass, though I
still love the overall laid back sound. Whenever I switch to my 770s for location work
I'm always shocked by how harsh they are in comparison!
Anyway, to answer your
question, the 880 is noticeably better and worth the extra money, but it depends if you
need them for tracking too. I prefer the edition version of the 880 because they're far
more comfortable to wear than the 'pro'.