Don't expect that the amplifier will sound very good suddenly with 600 hours of break in! Otherwise it would be magic. Do you believe in magic?
If you do a search I think you will find that it takes a lot of hours before the unit finds it final sound. 600-1000 hours sounds familiar. The designers have stated as much in an article or comment I read some time ago, so be patient. A lot of users seem to love it, so they must know what they are talking about.