Perhaps this opinion is not one that is going to be popular...but here it is..
IF you have to burn in something for 600 hours...for it to sound good, then I think something is very wrong. How can anyone remember exactly how something sounds from the past when that memory is now 600 hours old?
I have an a’phile friend who owns a ARC preamp with the Teflon caps...tells me it takes up to 1500 hours to burn in and for it to sound good!! 1500 hours...that is several YEARS in many systems running time!!!
Personally, I think that it is possible that a component can sound good from the gitgo and get better as time goes by, BUT IF it sounds poor from the gitgo...and 600 hours later it does not...is this not perhaps an acceptance of the SQ from a psychological perspective after all of that time? Inquiring minds...