Actually, if he replayed the mp3's on the Amiga with some crap AHI-settings and/or bad mp3-decoder, then the IFF-file might actually sound better on the Amiga 
Actually that is true... I had an integer decoder that played mp3's in "real time" that sounded horrible compared to the "offline" floating point decoder that converted the mp3 to a wav file (if my memory serves).