Here's the short answer: Flacs that are properly tagged with jpeg art work very well on the AK120 and it's fairly easy to do on a mac. You get sorting by album and artist (the AK120 only reads the tags, not the file or folder names) and you get nice album art on the screen while playing the music. There is currently no way to create playlists on the mac for the AK120.
I finally bit the bullet to get my music together on my mac for the AK120.
First of all, I did listening tests. Flac and WAV were indistinguishable. But downsampling and further compression sounded ever so slightly worse through the UltimateEars Reference Monitors.
DSD files did not sound better than flacs to me and they made the AK120 hot, sluggish and reduced battery life.
I have tons of HD music from DVD-Audio Extractor (my collection). Some of these are at 24/192, which I consider overkill, but I haven't taken the time to downsample them to make more room.
I've also been ripping SACD's using a PS3 and Korg Audiogate to create flacs in 24/88.2.
Then there are my Vinyl rips, using a Sound Devices 702 (my old 'portable' player), and various downloads from HDTracks. Most of this was in WAV format.
(If any of the above is technically illegal they can come and arrest me. These are my disks and my personal use!)
I created a new folder called HDMusic and copied all of the music I wanted on the AK120 to it. Since it's a copy I felt bold enough to experiment. I used xACT to create flacs from all of my WAV and other non-flac files and deleted the WAV's.
I used Tag to fix all of the tagging problems and add Album art. 500x500 Jpegs in the folders did not work for the WAV files on the AK120. But it made sure I had everything handy when I used Tag.
Then I made four subfolders of <62GB to copy to the various storage devices. - I have 3 cards and the internal memory. Unfortunately I have to rescan the library every time I change cards. But I try to keep that to a minimum. Be sure to leave enough room on the internal memory for the catalog. It gets big when you have 192GB of music with album art.
I also ordered a SD>MicroSD adapter that I'll experiment with when it arrives. Maybe I can get everything loaded at once.
Vox is a great mac flac player and very helpful in flight checking your tracks to make sure that everything will work on the AK120. So far if something is properly tagged it shows up the same in Vox as on the AK120. There is one exception here. If your art was a png file you need to convert it to jpeg if you want to to show up on the AK120.
Vox and Tag are available on the iTunes App Store, and you can google the other software. I checked, it comes right up.
Now my AK120 works exactly as it should and I have the bonus of enjoying flacs directly on my mac. (The Meridian Explorer sounds slightly better than the AK120, but it's not portable.) Yes, this took several hours but that's why they call this a hobby.
I hope this helps. Good Luck!
Edited by Sam Edwards - 11/25/13 at 9:59am