What defines mid-fi versus high-end?

If anyone bothered to listen to the one hour 45 minute YouTube interview with founder of Merrill Audio that user danager posted above, they would be treated to a discussion of real High Fidelity as he advertised. A discussion of how “I did it myself because I didn’t see anyone else doing it” (paraphrasing Merrill), “the weaknesses of other’s approach is . . .” (again, paraphrasing), and “with my approach, the challenges were ‘a,’ ‘b,’ ‘c,’ which we met by doing ‘x,’ ‘y,’ ‘x.’” (Once more, paraphrasing). Really intelligently laying out the challenges which every audio engineer must meet and overcome. We have our transformers custom made, and our supplier won’t tell us how they do it, but they meet our specifications. One of our competitors (and friends), has his capacitors made to his specifications and tests each one. What are the plates on top of the case? They help with the vibrations in the case— I could go on. But, the point is, the ultimate product is sound like no one has ever heard before. That is High Fidelity, because someone cares, because everything matters. And yes, it costs five figures (but not six), so yes, it is expensive, like it always was, it it is attainable, given a lifetime, or the greater portion of it.

"High End" refers only to price.

"Mid Fi" refers to the current system of all audiophiles.

'Mid-Fi' is an arbitrary marketing term thrown about loosely by those with something to gain by creating artificial barriers to entry. And painting products, even entire brands with that brush, they hope to justify there own products and brands exorbitant pricing. Case in point is Marantz. Their products span pricing from $500 to $10,000. A $500 receiver is of necessity a cost engineered product; a $9,000 integrated  amp, decidedly less so, and clearly a 'high-end' product. Yet despite impeccable technical execution, I have heard it derided as 'too mid-fi'. That is simple snobbery with some unacceptable implied overtones.

Does it matter what you or others call it? If you are entertained by and enjoy it...

The key is to get the best sound reproduction for YOU within your budget.

Answer: your income.  What you can afford is seen inevitably as the "low-end" of audiophilia.  The highest end is always to dream for, whether $5,000 or $500,000.  Does really high quality sound demand that?  No, not at all.  But human nature does.