sennheisers have better build quality
FWIW I had the 681 EVO and had to return them. They sounded very good, but with any head movement they creaked, driving me crazy. Never heard the HD439.
i thought the 681's were ok, SQ wise but they felt like trash in my hand. IMO they are "that" bad. :( unfortunately.
I recommend the Koss KSC75 with the headband mod. Unless you like earclips(the way they come). Cheaper than the 681EVO and sound better.
I have had the 681 EVOs for 6 months, and I really haven't had any issues with the build quality. I really don't know what these people are talking about.
This is what happen to my Evo 681 after less than 6 month. Just be careful. Planning an upgrade to HD 439.