First and foremost I have never used a MAc and cannot verify this 100%, but am trying to help a fellow 8120 user(just switched from one to my 8900). I always found the media manager crap to be a painand after trying it a time or 2 gave up for good. Most computer, even Macs have either an sd reader, or a USB port. I am assuming you have a media card, right?? Surely if your storing music, you do, as there is so little room to store such things on an, 8120(without some major mods, that may void warranty). Back on subject, I just use either my sd card reader and drag n drop the files directly into the music file on my sd card.
How to do this:
1. (Power off if needed my sd card has a side door so i dont power down)Remove miscro sd
2. Insert micro sd into either a USB microsd card reader.
into the card adapter and then the sd card slot on your Mac
3. it should auto play and /or open that drive
4. Click and open the blackberry file
5. Click and open the music file.
6. Highlight drag and drop your music files into this folder.
7. Eject the card
8. Put back in your 8120/allowing time to load
9. Enjoy your music.
Hope this helps . .