Sprogget:
I gave you the wrong poop! (Must be my advancing age.)
The Mac-centric files are .dmg files. not .img.
There are several software packages which will convert .img files to .iso but you've referenced most of them.
Have you tried changing the file extension from .img to .iso and see what happens.
Also, when using MagicISO did you ensure the "Standard ISO Image file (.ISO)" was selected at the output format?
If this file was ftp'd I hope it was done so using binary and not ascii!!!