M4A is an Apple thing so I, inherently, don't trust it. All the stuff I read about it was comparing stuff compressed at 128kbs and that's really not a great sound in any format.
I don't use Apple, I never liked their proprietary/costly business model. Plus over a 30 year career, I never saw a single engineering dept. use Apple computers. Vax, Unix, Windows and various mainframe supercomputers such as Cray but never Apple. Apple has always been an innovative company but I'm a dyed-in-the-wool Windows guy.
I understand Apple
did develop the M4A format to succeed MP3 and so far I'm seeing no problems with it. Studio One can export in that format, Windows Media Player can play them and I understand SoundCloud will except them.
Based on new info acquired, I updated my signal diagram.