Well I figure that I have about 100 hours on my new anthem MCA 225 power amp & it took awhile to break in as it seemed a little bright on the upper range,but must admit that the more that I have used it has really smoothed out & no issues as far as power goes & it barely gets warm even if you have session to test volume, distortion, music compatability,it still is a tad bright in the upper range but after listening to the NAD C 275 Bee for 4 years it's a bit of an adjustment but not in a bad way, stereo seperation is amazing & the sound stage is about a good foot & a half wider than the NAD,the bass is not as boomy it's more tightly controlled all in all a good purchase as music is food for the soul I can't stand bad sounding cheap big box store systems when for a bit more money & education on the choices that are available out there will provide you with a lifetime of enjoyment I consider it an investment.
I'd only like to add that break in is one of those 3rd rail topics. But that being said, I DO believe that capacitors break in. It's called 'forming'. Do other parts break in? I don't know, but the next step is to adjust SETUP which may also change with the new amp. By setup I mean the fine-tuning of speaker position and toe-in.