Just picked up some CALs for work. Do they require much of a break in period?
Just play them bro. I'll say tho that the Denon AHD-1000/CAL are the only headphone I've ever noticed " Burn In".
My Denon's I got at the beginning of 09 and sound better then most cans up to the $200 mark. I never put a "Time" on break in but you will notice changes for sure with the Cal's. And it's not just " In your head" so to speak.