sold my first set of xlr cardas gr's after about 72 hours of use. hated them and didn't see any need to go on. was talked into trying them again but going 150 hours before listening and making a choice. they sounded much better but still not that great. high's still sounded a bit "veiled", as others have stated in the past.
continued shopping and demo's for a few weeks but kept the gr's around to compare with. tried 6 different/comperable xlr ic's. during that time the gr's got another 100+ hours on them.
couldn't believe how they opened up, especially up top. all of sudden i had detail along with crisp/clear sound up high?. went from "hate" too "pretty damn good!"??. they ended up being the best (so far) for my system. never would have guessed this from the first 150 hours.
my long, drawn out point is....i'd give them a good while to settle in. if you want to hear what they can do, give them 250+ hours first...then decide. sounds like a crazy amount of time imo but that's how it went for me and my system.
tried the extended break-in on several of the other ic's but didn't get the same result (az silver ref2 and matrix 2, tara rsc air 2's, audioquest colorado). they seemed all in after about 150 hours with little/no change after that. i've got no explanation for this either.
