Hi jtcf
Here's a rule of thumb (a broadly accurate guide or principle, based on experience or practice rather than theory). Anytime you read someone can not hear breakin (burnin) "run". If someone is not able to hear audio differences in this hobby, they're the last one you should be taking sound advice from.
On this forum, and others, there are folks who come up and write purely for the sake of being noticed or boredom. Fact is, audio is a process that is in a continuum of change. Every second you listen change is happening. Learning to practice and play our systems is where we will find the sound that the "non-doers" will never have.
Don't pay attention to those who say they have been doing this hobby for 40 years, it means zero if they can't hear a simple thing like burnin. If a hobbyist can't hear burnin it means one of two things. One, their system is full of signal blockage (a common problem with HEA systems), and two, they simply can not hear the change. In either case they are not qualified to give advice on something they haven't experienced.
Debating if burnin exist is like asking a vegetarian how a burger taste.
anyway, now I'm hungry
Michael Green