Oh yeah, I think brain burn-in is the most important part of it all, I had IEM's that I didn't like a first and thought I might sale them but after a few days of brain burn-in I loved the IEM (it was the Earsonics SM3 V2)
The reason I want the HD600 is because its more laid back compared to the HE-400 but its not as warm as the HD650, I read where more people like the HD600 over the HD650. With those 2 HP's I'll be set for awhile once I get my Schiit Asgard 2 amp.
I didn't expect to just jump-in head first into headphones like I have but after the first day listening to the HE-400 I was hooked and most of my IEM's are being sold except a couple.