Just received my first pair of Grado brand cans! Got them on ebay for $220. They were gently used. Serial #2364. No box though.
I believe these have the truest sound of all the cans I own. Ultrasone Pro750; Ultrasone 2900(currently being repaired); Sony MDR-1; and Audio-Technica AD900's(bought from another Head-fier).
The soundstage is a bit lacking but they're definitely not colored in any way. I really dig this sound!
I believe as I use each of my cans I will be able to figure out which pair sounds best for each genre of music I own. I think so far that these will be really good for rock and prog rock. I found that the female vocals are a bit recessed for my taste. Male vocals sound perfect though. Guitars really crunch! Nice bass also...again true not colored.
I'm not sure how many hours burn in they have had so not sure if the sound will change much. So far so good!
Congrats! I wouldn't worry so much about burn in for these. According to Grado, it doesn't need much time nor effort for the sound to settle so just enjoy.