Well, I almost feel guilty of having iniciated such a fire with my rather innocent comment....
My friend, he is brilliant, a science mind, and his statement is based on factual science (as many people have argued).
Me, not a scientist, but someone who has been raised with audio gear around. My father owned a bit of hi fi gear:thorens turntabler, sm tonearm, Shure magnetic coils, Nakamichi, Stax headphones, etc..... That was forty years ago....I had myself bought the best audio I could afford:Stax SR-5 headphones, Harman Kardon hifi gear, mission speakers, I even had a baby stax and a high end sony portable cd player....
Lately I had lost the interest in music. I had an ipad classic but I was missing the sounds from the cds.....although. I was not aware of this...
Then I stepped by chance on the issue of Flac files and DAPs like fiio. I gave it a try and I was shocked to see the difference between the X3 and the ipod classic. I could see (read hear) the difference, it was shouting at me....
So although my brain tells me my friend is right, my heart/ear tells me he is wrong....
But the only way to know it for sure is trying a blind taste of mp3 vs flac, hd tracks vs cds, ipods vs fiios, etc.......