Well, I have my new HD380 Pro's. I have burned them in for around 100hrs and have a further 150hrs of listening on them. I would like to share my thoughts on them in comparison to the HD 280 Pro and ATH-M50s.
They have turned out to be my new day to day use headphone and I am considering selling my ATH-M50 and HD280.
They do exactly what I was hoping for which is:
Have a similar sound signature to the HD280 but much more refined.
Provide deep tight bass - Better so than the ATH-M50 and comparible with the HD280 but more detailed. They are in no way loose and flabby like the ATH -M50. Kick drums really have a nice snap to them. I would say that the bass is slightly exaggerated but not offensively so.
They provide more mid range than the ATH-M50 and less than the HD280 giving vocals and guitars plenty of texture and weight without sounding harsh.
They have less treble than the ATH-M50 and more than the HD280. I find with the ATH-M50 to have the volume set at a comfortable listening level so that the music has sufficient impact the treble is too harsh, turn down the volume and the bass is lacking as are the mids. Treble was always a bit lacking on the HD280.
I like these Headphones and think they are a keeper.