I keep going back and forth with myself on whether I want to exchange them or just return them and save up for a Beyerdynamic T1. But listening again, these really do sound pretty good. I just don't want to deal with the hassle. But I think they are pretty good... I might just try to get some HD650s for a good price and try to sell my HD600s. I like the sound a lot but they're just a little too closely sounding to the HE400s for me to decide which one to listen to. Plus... I got a Lyr and I have a Bifrost on the way. I feel like the HD650s will shine with this combo, even more than the HD600s.
My one advice is you have to listen to the "fixed" version of HE400s before making any judgements. In my opinion it's a huge improvement from this defective rev3 treble. Hifiman already promised they will pay for the replacement shipping both ways, so it does not hurt at all for anyone with rev3 to do this.