I’m about 35 hours in on breaking the 820 in, and I’m not hearing anything really different than I heard after 8 hours, maybe a very subtle difference, but I can’t honestly say I do.
I’m running these thru the matching HDV 820 amp in balanced mode. I’ve been listening to all genres of music, from jazz, classical, rock and blues. Everything sounds superb. Wide, detailed soundstage, deep, solid natural sounding bass response and smooth, detailed treble. Vocals are fantastic, like your hearing the direct feed from the mic. Separation and spatiality are all there. My pair fit my head perfectly, snug but not too tight. Extremely comfortable, and they do not warm up with hours of use.
I also have the 800S, which is a wonderful headphone, but the 820 gives me more bass and slam, with nearly all the widescreen sound of the S800.
Both are really phenomenal sets of cans, but to me the 820 is now my reference headphone.